description: You are given a book with n chapters.
  
  Each chapter has a specified list of other chapters that need to be understood in order to understand this chapter. To understand a chapter, you must read it after you understand every chapter on its required list.
  
  Currently you don't understand any of the chapters. You are going to read the book from the beginning till the end repeatedly until you understand the whole book. Note that if you read a chapter at a moment when you don't understand some of the required chapters, you don't understand this chapter.
  
  Determine how many times you will read the book to understand every chapter, or determine that you will never understand every chapter no matter how many times you read the book.
  
  Input
  
  Each test contains multiple test cases. The first line contains the number of test cases t (1 ≤ t ≤ 2⋅10^4).
  
  The first line of each test case contains a single integer n (1 ≤ n ≤ 2⋅10^5) — number of chapters.
  
  Then n lines follow. The i-th line begins with an integer k_i (0 ≤ k_i ≤ n-1) — number of chapters required to understand the i-th chapter. Then k_i integers a_{i,1}, a_{i,2}, ..., a_{i, k_i} (1 ≤ a_{i, j} ≤ n, a_{i, j} ≠ i, a_{i, j} ≠ a_{i, l} for j ≠ l) follow — the chapters required to understand the i-th chapter.
  
  It is guaranteed that the sum of n and sum of k_i over all testcases do not exceed 2⋅10^5.
  
  Output
  
  For each test case, if the entire book can be understood, print how many times you will read it, otherwise print -1.
  
  Example
  
  Input
  
  
  5
  4
  1 2
  0
  2 1 4
  1 2
  5
  1 5
  1 1
  1 2
  1 3
  1 4
  5
  0
  0
  2 1 2
  1 2
  2 2 1
  4
  2 2 3
  0
  0
  2 3 2
  5
  1 2
  1 3
  1 4
  1 5
  0
  
  
  Output
  
  
  2
  -1
  1
  2
  5
  
  Note
  
  In the first example, we will understand chapters \{2, 4\} in the first reading and chapters \{1, 3\} in the second reading of the book.
  
  In the second example, every chapter requires the understanding of some other chapter, so it is impossible to understand the book.
  
  In the third example, every chapter requires only chapters that appear earlier in the book, so we can understand everything in one go.
  
  In the fourth example, we will understand chapters \{2, 3, 4\} in the first reading and chapter 1 in the second reading of the book.
  
  In the fifth example, we will understand one chapter in every reading from 5 to 1.
solution: import java.sql.SQLSyntaxErrorException;
  import java.util.*;
  import java.io.*;
  import java.util.stream.StreamSupport;
  
  
  public class Solution {
      static int mod = 998244353;
      public static void main(String str[]) throws IOException{
  //        Reader sc = new Reader();
          BufferedWriter output = new BufferedWriter(new OutputStreamWriter(System.out));
          Scanner sc = new Scanner(System.in);
          int t = sc.nextInt();
          sc.nextLine();
          int a = 1;
          while(t-->0){
              int n= sc.nextInt();
              Node[] nodes = new Node[n];
              for(int i=0;i<n;i++){
                  nodes[i] = new Node(i);
              }
              for(int i=0;i<n;i++){
                  int x = sc.nextInt();
                  while(x-->0){
                      int ind = sc.nextInt()-1;
                      nodes[ind].child.add(nodes[i]);
                      nodes[i].parent.add(nodes[ind]);
                  }
              }
              ArrayList<Integer> al = new ArrayList<>();
              for(int i=0;i<n;i++){
                  if(nodes[i].parent.isEmpty())   al.add(i);
              }
              for(int i: al){
                  dfs(nodes, nodes[i],null);
              }
              int ans =0;
              for(int i=0;i<n;i++){
                  if(!nodes[i].parent.isEmpty()){
                      ans = -1;
                      break;
                  }
                  ans = Math.max(ans, nodes[i].tot);
              }
              System.out.println(ans);
          }
  
  
          output.flush();
      }
      static class Pair {
          int ind;
          char c;
          Pair(int i, char v) {
              ind = i;
              c = v;
          }
      }
  
      //Collections.sort(al, new Comparator<Object>() {
      //    @Override
      //    public int compare(Object o1, Object o2) {
      //        return 0;
      //    }
      //});
  
      static class Node{
          int ind;
          int tot = 1;
          ArrayList<Node> parent = new ArrayList<>();
          ArrayList<Node> child = new ArrayList<>();
          Node(int i){
              ind =i;
          }
      }
      static void dfs(Node[] nodes, Node ind, Node parent){
          if(parent!=null){
              ind.parent.remove(parent);
              int x = parent.tot;
              if(parent.ind>ind.ind){
                  x++;
              }
              ind.tot = Math.max(x, ind.tot);
          }
          if(ind.parent.isEmpty()){
              for(Node n: ind.child){
                  dfs(nodes, n, ind);
              }
          }
  
      }
      static int maxHeight(List<Integer> wallPositions, List<Integer> wallHeights){
          int ans = 0;
          int n = wallHeights.size();
          for(int i=1;i<n;i++){
              int ind1 = wallPositions.get(i-1);
              int ind2 = wallPositions.get(i);
              if(ind2-ind1==1)    continue;
              int x = wallHeights.get(i-1);
              int y = wallHeights.get(i);
              int index = (y-x+ind1+ind2)/2;
              if(index<=ind1){
                  index = ind1+1;
              }
              else if(index>=ind2){
                  index = ind2-1;
              }
              ans = Math.max(ans, Math.min(x+(index-ind1),y+(ind2-index)));
          }
          return ans;
      }
  
  
  
  
  //        3
  //        2 1 1
  //        2 3 1
  //        3 4 1
  //        4
  //        2
  
  
      public static ArrayList<Integer> primeFactors(int n)
      {
          // Print the number of 2s that divide n
          ArrayList<Integer> al = new ArrayList<>();
          while (n%2==0)
          {
              al.add(2);
              n /= 2;
          }
  
          // n must be odd at this point.  So we can
          // skip one element (Note i = i +2)
          for (int i = 3; i <= Math.sqrt(n); i+= 2)
          {
              // While i divides n, print i and divide n
              while (n%i == 0)
              {
                  al.add(i);
                  n /= i;
              }
          }
  
          // This condition is to handle the case whien
          // n is a prime number greater than 2
          if (n > 2)
              al.add(n);
  
          return al;
      }
  
  
  
  
      static void bfs(Graph[] g, int ind, boolean vis[], ArrayList<Node> al, Set<Integer> set){
          vis[ind] = true;
          set.add(ind);
          for(int i: g[ind].pq){
              if(!vis[i])     bfs(g,i,vis,al,set);
          }
          g[ind].set = set;
      }
  
  
  //    static class tempSort implements Comparator<Node> {
  //        // Used for sorting in ascending order of
  //        // roll number
  //        public int compare(Node a, Node b) {
  //            return a.size - b.size;
  //        }
  //    }
  
  
  
  
  
      static long divide(long p, long q, long mod)
      {
          long expo = mod - 2;
  
          while (expo != 0)
          {
              if ((expo & 1) == 1)
              {
  //                long temp = p;
  //                System.out.println("zero--> "+temp+" "+q);
                  p = (p * q) % mod;
  //                if(p<0){
  //                    System.out.println("one--> "+temp+" "+q);
  //                }
              }
              q = (q * q) % mod;
  //            if(q<0){
  //                System.out.println("two--> "+p+" "+q);
  //            }
  
              expo >>= 1;
          }
          return p;
      }
  
  
      static class Graph{
          int ind;
          ArrayList<Integer> pq = new ArrayList<>();
          Set<Integer> set;
          boolean b = false;
          public Graph(int a){
              ind = a;
          }
  
  
      }
  
  
      //
  //    static class Pair{
  //        int a=0;
  //        int b=0;
  //        int in = 0;
  //        int ac = 0;
  //        int ex = 0;
  //    }
      long fun2(ArrayList<Integer> arr, int x){
          ArrayList<ArrayList> al = new ArrayList<>();
          ArrayList<Integer> curr = new ArrayList<>();
          fun(arr, x, al, curr, 0);
          if(al.size()==0)    return 0;
          int max = 0;
          for(ArrayList<Integer> i: al){
              if(i.size()>max)    max = i.size();
          }
          for(int i=0;i<al.size();i++){
              if(al.get(i).size()!=max){
                  al.remove(i);
                  i--;
              }
          }
          for(ArrayList<Integer> i: al){
              Collections.sort(al, Collections.reverseOrder());
          }
          long ans = 0;
  
          for(ArrayList<Integer> i: al){
              long temp = 0;
              for(int j: i){
                  temp*=10;
                  temp+=j;
              }
              if(ans<temp)    ans = temp;
          }
          return ans;
  
      }
      void fun(ArrayList<Integer> arr, int x, ArrayList<ArrayList> al, ArrayList<Integer> curr, int i){
          if(x<0) return ;
          if(x==0) {
              al.add(curr);
              return;
          }
          for(int j=i;j<arr.size();j++){
              ArrayList<Integer> temp = new ArrayList<>(curr);
              fun(arr, x-arr.get(j), al, temp, j);
          }
      }
  
  
  
      // Returns n^(-1) mod p
      static long modInverse(long n, long p)
      {
          return (long)power(n, p - 2, p);
      }
  
  
  
      // Returns nCr % p using Fermat's
      // little theorem.
      static long nCrModPFermat(int n, int r,
                                int p, long[] fac)
      {
  
          if (n<r)
              return 0;
          // Base case
          if (r == 0)
              return 1;
  
          // Fill factorial array so that we
          // can find all factorial of r, n
          // and n-r
          long x = modInverse(fac[r], p);
          long y = modInverse(fac[n - r], p);
  
          return (fac[n] * x
                  % p * y
                  % p)
                  % p;
      }
  
      static long[] sum(String[] str){
          int n = str[0].length();
          long ans[] = new long[n];
          for(String s: str){
              for(int i=0;i<n;i++)   ans[i]+=s.charAt(i);
          }
          return ans;
      }
  
  //    static class tSort implements Comparator<Pair>{
  //
  //        public int compare(Pair s1, Pair s2) {
  //            if (s1.b < s2.b)
  //                return -1;
  //            else if (s1.b > s2.b)
  //                return 1;
  //            return 0;
  //        }
  //    }
  
  
  //    static boolean checkCycle(Tree[] arr,  boolean[] visited, int curr, int node){
  //        if(curr==node && visited[curr]) return true;
  //        if(visited[curr])   return false;
  //        visited[curr]  = true;
  //        for(int i: arr[curr].al){
  //            if(checkCycle(arr, visited, i, node))    return true;
  //        }
  //        return false;
  //    }
  
  
  //    static boolean allCombinations(int n){      //Global round 15
  //        int three2n = 1;
  //        for (int i = 1; i <= n; i++)
  //            three2n *= 3;
  //
  //        for (int k = 1; k < three2n; k++) {
  //            int k_cp = k;
  //            int sum = 0;
  //            for (int i = 1; i <= n; i++) {
  //                int s = k_cp % 3;
  //                k_cp /= 3;
  //                if (s == 2) s = -1;
  //                sum += s * a[i];
  //            }
  //            if (sum == 0) {
  //                return true;
  //            }
  //        }
  //        return false;
  //    }
  
      static ArrayList<String> fun( int curr, int n, char c){
          int len = n-curr;
          if(len==0)  return null;
          ArrayList<String> al = new ArrayList<>();
          if(len==1){
              al.add(c+"");
              return al;
          }
          String ss = "";
          for(int i=0;i<len/2;i++){
              ss+=c;
          }
          ArrayList<String> one = fun(len/2+curr, n, (char)(c+1));
          for(String str: one){
              al.add(str+ss);
              al.add(ss+str);
          }
          return al;
      }
      static ArrayList convert(int x, int k){
          ArrayList<Integer> al = new ArrayList<>();
          if(x>0) {
              while (x > 0) {
                  al.add(x % k);
                  x /= k;
              }
          }
          else    al.add(0);
          return al;
      }
  
  
  
  
      static int max(int x, int y, int z){
          int ans = Math.max(x,y);
          ans = Math.max(ans, z);
          return ans;
      }
      static int min(int x, int y, int z){
          int ans = Math.min(x,y);
          ans = Math.min(ans, z);
          return ans;
      }
  
  //    static long treeTraversal(Tree arr[], int parent, int x){
  //        long tot = 0;
  //        for(int i: arr[x].al){
  //            if(i!=parent){
  //                tot+=treeTraversal(arr, x, i);
  //            }
  //        }
  //        arr[x].child = tot;
  //        if(arr[x].child==0) arr[x].child = 1;
  //        return tot+1;
  //    }
  
      public static int primeFactors(int n, int k)
      {
          int ans = 0;
  
          while (n%2==0)
          {
              ans++;
              if(ans>=k)  return k;
              n /= 2;
          }
          for (int i = 3; i <= Math.sqrt(n); i+= 2)
          {
              while (n%i == 0)
              {
                  ans++;
                  n /= i;
                  if(ans>=k)  return k;
              }
          }
  
          if (n > 2)  ans++;
          return ans;
      }
      static int binaryLow(ArrayList<Integer> arr, int x, int s, int e){
          if(s>=e){
              if(arr.get(s)>=x)  return s;
              else    return s+1;
          }
          int m = (s+e)/2;
          if(arr.get(m)==x)  return m;
          if(arr.get(m)>x)   return binaryLow(arr,x,s,m);
          if(arr.get(m)<x)   return binaryLow(arr,x,m+1,e);
          return 0;
      }
      static int binaryLow(int[] arr, int x, int s, int e){
          if(s>=e){
              if(arr[s]>=x)  return s;
              else    return s+1;
          }
          int m = (s+e)/2;
          if(arr[m]==x)  return m;
          if(arr[m]>x)   return binaryLow(arr,x,s,m);
          if(arr[m]<x)   return binaryLow(arr,x,m+1,e);
          return 0;
      }
      static int binaryHigh(int[] arr, int x, int s, int e){
          if(s>=e){
              if(arr[s]<=x)  return s;
              else    return s-1;
          }
          int m = (s+e)/2;
          if(arr[m]==x)  return m;
          if(arr[m]>x)   return binaryHigh(arr,x,s,m-1);
          if(arr[m]<x)   return binaryHigh(arr,x,m+1,e);
          return 0;
      }
  
  
  //    static void arri(int arr[], int n, Reader sc) throws IOException{
  //        for(int i=0;i<n;i++){
  //            arr[i] = sc.nextInt();
  //        }
  //    }
  //    static void arrl(long arr[], int n, Reader sc) throws IOException{
  //        for(int i=0;i<n;i++){
  //            arr[i] = sc.nextLong();
  //        }
  
  
      static long gcd(long a, long b)
      {
          if (b == 0)
              return a;
          return gcd(b, a % b);
      }
      static long power(long x, long y, long p)
      {
          long res = 1; // Initialize result
  
          x = x % p; // Update x if it is more than or
          // equal to p
  
          if (x == 0)
              return 0; // In case x is divisible by p;
  
          while (y > 0)
          {
  
              // If y is odd, multiply x with result
              if ((y & 1) != 0)
                  res = (res * x) % p;
  
              // y must be even now
              y = y >> 1; // y = y/2
              x = (x * x) % p;
          }
          return res%p;
      }
  
  
  
  
  
  
  //    static class SortbyI implements Comparator<Pair> {
  //        // Used for sorting in ascending order of
  //        // roll number
  //        public int compare(Pair a, Pair b)
  //        {
  //            if(a.a>=b.a) return 1;
  //            else return -1;
  //        }
  //    }
  //    static class SortbyD implements Comparator<Pair> {
  //        // Used for sorting in ascending order of
  //        // roll number
  //        public int compare(Pair a, Pair b)
  //        {
  //            if(a.a<b.a) return 1;
  //            else if(a.a==b.b && a.b>b.b)    return 1;
  //            else return -1;
  //        }
  //    }
  //    static int binarySearch(ArrayList<Pair> a, int x, int s, int e){
  //        if(s>=e){
  //            if(x<=a.get(s).b)  return s;
  //            else    return s+1;
  //        }
  //        int mid = (e+s)/2;
  //        if(a.get(mid).b<x){
  //            return binarySearch(a, x, mid+1, e);
  //        }
  //        else    return binarySearch(a,x,s, mid);
  //    }
  
      //    static class Edge{
  //        int a;
  //        int b;
  //        int c;
  //        int sec;
  //        Edge(int a, int b, int c, int sec){
  //            this.a = a;
  //            this.b = b;
  //            this.c = c;
  //            this.sec = sec;
  //        }
  //
  //    }
      static class Tree{
          int a;
  
          ArrayList<Tree> al = new ArrayList<>();
          Tree(int a){
              this.a = a;
          }
  
  
      }
  
      static class Reader {
          final private int BUFFER_SIZE = 1 << 16;
          private DataInputStream din;
          private byte[] buffer;
          private int bufferPointer, bytesRead;
  
          public Reader()
          {
              din = new DataInputStream(System.in);
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public Reader(String file_name) throws IOException
          {
              din = new DataInputStream(
                      new FileInputStream(file_name));
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public String readLine() throws IOException
          {
              byte[] buf = new byte[64]; // line length
              int cnt = 0, c;
              while ((c = read()) != -1) {
                  if (c == '\n') {
                      if (cnt != 0) {
                          break;
                      }
                      else {
                          continue;
                      }
                  }
                  buf[cnt++] = (byte)c;
              }
              return new String(buf, 0, cnt);
          }
  
          public int nextInt() throws IOException
          {
              int ret = 0;
              byte c = read();
              while (c <= ' ') {
                  c = read();
              }
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          public long nextLong() throws IOException
          {
              long ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
              if (neg)
                  return -ret;
              return ret;
          }
  
          public double nextDouble() throws IOException
          {
              double ret = 0, div = 1;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
  
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (c == '.') {
                  while ((c = read()) >= '0' && c <= '9') {
                      ret += (c - '0') / (div *= 10);
                  }
              }
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          private void fillBuffer() throws IOException
          {
              bytesRead = din.read(buffer, bufferPointer = 0,
                      BUFFER_SIZE);
              if (bytesRead == -1)
                  buffer[0] = -1;
          }
  
          private byte read() throws IOException
          {
              if (bufferPointer == bytesRead)
                  fillBuffer();
              return buffer[bufferPointer++];
          }
  
          public void close() throws IOException
          {
              if (din == null)
                  return;
              din.close();
          }
      }
  
  
      static boolean isPrime(int n)
      {
          if (n <= 1)
              return false;
          if (n <= 3)
              return true;
          if (n % 2 == 0 ||
                  n % 3 == 0)
              return false;
  
          for (int i = 5;
               i * i <= n; i = i + 6)
              if (n % i == 0 ||
                      n % (i + 2) == 0)
                  return false;
  
          return true;
      }
      static ArrayList<Integer> sieveOfEratosthenes(int n)
      {
          ArrayList<Integer> al = new ArrayList<>();
          // Create a boolean array
          // "prime[0..n]" and
          // initialize all entries
          // it as true. A value in
          // prime[i] will finally be
          // false if i is Not a
          // prime, else true.
          boolean prime[] = new boolean[n + 1];
          for (int i = 0; i <= n; i++)
              prime[i] = true;
  
          for (int p = 2; p * p <= n; p++)
          {
              // If prime[p] is not changed, then it is a
              // prime
              if (prime[p] == true)
              {
                  // Update all multiples of p
                  for (int i = p * p; i <= n; i += p)
                      prime[i] = false;
              }
          }
  
          // Print all prime numbers
          for (int i = 2; i <= n; i++)
          {
              if (prime[i] == true)
                  al.add(i);
          }
          return al;
      }
  
  }
  