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.io.BufferedReader;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.*;
  import java.io.PrintStream;
          
              public class Solution {
  
                  public static boolean Local(){
                      try{ 
                          return System.getenv("LOCAL_SYS")!=null;
                      }catch(Exception e){
                          return false;
                      }
                  }   
  
                  public static boolean LOCAL;
  
                  static class FastScanner {
  
                          BufferedReader br;
                          StringTokenizer st ;
  
                          FastScanner(){
                              br =  new BufferedReader(new InputStreamReader(System.in));
                              st = new StringTokenizer("");
                          }
  
                          FastScanner(String file) {
  
                              try{
                                  br =  new BufferedReader(new InputStreamReader(new FileInputStream(file)));
                                  st = new StringTokenizer("");
                              }catch(FileNotFoundException e) {
                                  // TODO Auto-generated catch block
                                  System.out.println("file not found");
                                  e.printStackTrace();
                              }
                              
                          }
                          
  
                          String next() {
                              while (!st.hasMoreTokens())
                                  try {
                                      st = new StringTokenizer(br.readLine());
                                  } catch (IOException e) {
                                  }
                              return st.nextToken();
                          }
  
                          int nextInt() {
                              return Integer.parseInt(next());
                          }
  
                          long nextLong() {
                              return Long.parseLong(next());
                          }
                          String readLine() throws IOException{
                              return br.readLine();
                          }
                      }
                                          
                  static class Pair<T,X> {
  
                      T first;
                      X second;
                      
                      Pair(T first,X second){
                          this.first = first;
                          this.second = second;
                      }
  
                      @Override
                      public int hashCode(){
                          return Objects.hash(first,second);
                      }
  
                      @Override
                      public boolean equals(Object obj){
                          return obj.hashCode() == this.hashCode();
                      }
  
                  }
  
              
              static PrintStream debug = null;
              
              
              static long mod = (long)(Math.pow(10,9) + 7); 
              
  
              public static void main(String[] args) throws Exception {
                  
                  FastScanner s = new FastScanner();
  
                  LOCAL = Local();
  
                  
                  if(LOCAL){
                      s = new FastScanner("src/input.txt");
                      PrintStream o = new PrintStream("src/sampleout.txt");
                      debug = new PrintStream("src/debug.txt");
                      System.setOut(o);
                  }
  
                  
                  long mod = 1000000007;
  
              
                  int tcr = s.nextInt();                  
                  
                  StringBuilder sb = new StringBuilder();
  
  
                  for(int tc=0;tc<tcr;tc++){
                      
                      PriorityQueue<Integer> pq = new PriorityQueue<>();
  
                      int n = s.nextInt();
  
                      List<List<Integer>> list = new ArrayList<>();
  
                      for(int i=0;i<n;i++){
                          list.add(new ArrayList<>());
                      }
  
                      int indegree[] = new int[n];
  
                      for(int i=0;i<n;i++){
                          int k = s.nextInt();
                          indegree[i] = k;
                          if(k==0){
                              pq.add(i);
                          }
                          for(int j=0;j<k;j++){
                              int v = s.nextInt();
                              v--;
                              list.get(v).add(i);
                          }
                      }
  
                    
  
                      if(pq.size() == 0){
                          sb.append(-1);
                          sb.append('\n');
                          continue;
                      }
  
  
                      int read = 0;
  
                      PriorityQueue<Integer> next = new PriorityQueue<>();
  
                      Set<Integer> set = new HashSet<>();
  
                      while(!pq.isEmpty()){
  
                          
                          read++;
  
                          while(!pq.isEmpty()){
  
                              int curr = pq.poll();
  
                              set.add(curr);
  
                              for(int v : list.get(curr)){
                                  indegree[v]--;
                                  if((indegree[v]==0)){
                                      if(v < curr){
                                          next.add(v);
                                      }else{
                                          pq.add(v);
                                      }
                                  }
                              }
  
                          }
  
                          // debug(debug,set);
                          // dbg(debug,next);
  
                          pq = next;
                          next = new PriorityQueue<>();
                      }
  
                      if(set.size() == n){
                           sb.append(read);
                      }else{
                          sb.append(-1);
                      }
                      sb.append('\n');
                  }
  
                  print(sb.toString());
  
              }
  
              public static boolean inRange(int r1,int r2,int val){
                  return ((val >= r1) && (val <= r2));
              }
  
              static int len(long num){
                  return Long.toString(num).length();
              }
  
              static long mulmod(long a, long b,long mod)
              {
                  long ans = 0l;
                  
                  while(b > 0){
                      long curr = (b & 1l);
                      if(curr == 1l){
                          ans = ((ans % mod) + a) % mod;
                      }
                      
                      a = (a + a) % mod;
  
                      b = b >> 1;
                  }
  
                  return ans;
              }
  
  
              public static void dbg(PrintStream ps,Object... o) throws Exception{
                  if(ps == null){
                      return;
                  }
                  Debug.dbg(ps,o);
              }
  
              public static long modpow(long num,long pow,long mod){
  
                  long val = num;
                  long ans = 1l;
  
                  while(pow > 0l){
                      
                      long bit = pow & 1l;
  
                      if(bit == 1){
                          ans = (ans * (val%mod))%mod;
                      }
  
                      val = (val * val) % mod;
                      pow = pow >> 1;
                  }
  
                  return ans;
  
              }
  
              public static char get(int n){
                  return (char)('a' + n);
              }
  
              public static long[] sort(long arr[]){
                  List<Long> list = new ArrayList<>();
                  for(long n : arr){list.add(n);}
                  Collections.sort(list);
                  for(int i=0;i<arr.length;i++){
                      arr[i] = list.get(i);
                  }
                  return arr;
              }
  
              public static int[] sort(int arr[]){
                  List<Integer> list = new ArrayList<>();
                  for(int n : arr){list.add(n);}
                  Collections.sort(list);
                  for(int i=0;i<arr.length;i++){
                      arr[i] = list.get(i);
                  }
                  return arr;
              }
  
              // return the (index + 1)
              // where index is the pos of just smaller element
              // i.e count of elemets strictly less than num
              public static int justSmaller(long arr[],long num){
                  //  System.out.println(num+"@");
                  int st = 0;
                  int e = arr.length - 1;
          
                  int ans = -1;
          
                  while(st <= e){
          
                      int mid = (st + e)/2;
          
                      if(arr[mid] >= num){
                          e = mid - 1;
                      }else{
                          ans = mid;
                          st = mid + 1;
                      }
          
                  }
          
          
                  return ans + 1;
          
              }
              public static int justSmaller(int arr[],int num){
                  //  System.out.println(num+"@");
                  int st = 0;
                  int e = arr.length - 1;
          
                  int ans = -1;
          
                  while(st <= e){
          
                      int mid = (st + e)/2;
          
                      if(arr[mid] >= num){
                          e = mid - 1;
                      }else{
                          ans = mid;
                          st = mid + 1;
                      }
          
                  }
          
          
                  return ans + 1;
          
              }
              
              //return (index of just greater element)
              //count of elements smaller than or equal to num
  
              public static int justGreater(long arr[],long num){
                  int st = 0;
                  int e = arr.length - 1;
          
                  int ans = arr.length;
          
                  while(st <= e){
                      
                      int mid = (st + e)/2;
          
                      if(arr[mid] <= num){
                          st = mid + 1;
                      }else{
                          ans = mid;
                          e = mid - 1;
                      }
                  }
          
                  return ans;
          
              }
  
              public static int justGreater(int arr[],int num){
                  int st = 0;
                  int e = arr.length - 1;
          
                  int ans = arr.length;
          
                  while(st <= e){
                      
                      int mid = (st + e)/2;
          
                      if(arr[mid] <= num){
                          st = mid + 1;
                      }else{
                          ans = mid;
                          e = mid - 1;
                      }
                  }
          
                  return ans;
          
              }
          
              
  
              public static void println(Object obj){
                  System.out.println(obj.toString());
              }
  
              public static void print(Object obj){
                  System.out.print(obj.toString());
              }
  
              public static int gcd(int a,int b){
                  if(b == 0){return a;}
                  return gcd(b,a%b);
              }
  
              public static long gcd(long a,long b){
                  if(b == 0l){
                      return a;
                  }
  
                  return gcd(b,a%b);
              }
  
              public static int find(int parent[],int v){
                  if(parent[v] == v){
                      return v;
                  }
                  
                  return parent[v] = find(parent, parent[v]);
              }
  
          
  
              public static List<Integer> sieve(){
              
                      List<Integer> prime = new ArrayList<>();
  
                      int arr[] = new int[100001];
  
                  Arrays.fill(arr,1);
  
                  arr[1] = 0;
                  arr[2] = 1;
  
                  for(int i=2;i<=100000;i++){
                      
                      if(arr[i] == 1){
                          
                          prime.add(i);
  
                          for(long j = (i*1l*i);j<100001;j+=i){
                              arr[(int)j] = 0;
                          }
                      }
                  }
  
                  return prime;
              }
  
              static boolean isPower(long n,long a){
                  
                  long log = (long)(Math.log(n)/Math.log(a));
  
                  long power = (long)Math.pow(a,log);
  
                  if(power == n){return true;}
  
                  return false;
              }
  
  
              private static int mergeAndCount(int[] arr, int l,int m, int r)
              {
  
                  // Left subarray
                  int[] left =  Arrays.copyOfRange(arr, l, m + 1);
  
                  // Right subarray
                  int[] right = Arrays.copyOfRange(arr, m + 1, r + 1);
  
                  int i = 0, j = 0, k = l, swaps = 0;
  
                  while (i < left.length && j < right.length) {
                      if (left[i] <= right[j])
                          arr[k++] = left[i++];
                      else {
                          arr[k++] = right[j++];
                          swaps += (m + 1) - (l + i);
                      }
                  }
                  while (i < left.length)
                      arr[k++] = left[i++];
                  while (j < right.length)
                      arr[k++] = right[j++];
                  return swaps;
              }
  
              // Merge sort function
              private static int mergeSortAndCount(int[] arr, int l,int r)
              {
  
                  // Keeps track of the inversion count at a
                  // particular node of the recursion tree
                  int count = 0;
  
                  if (l < r) {
                      int m = (l + r) / 2;
  
                      // Total inversion count = left subarray count
                      // + right subarray count + merge count
  
                      // Left subarray count
                      count += mergeSortAndCount(arr, l, m);
  
                      // Right subarray count
                      count += mergeSortAndCount(arr, m + 1, r);
  
                      // Merge count
                      count += mergeAndCount(arr, l, m, r);
                  }
  
                  return count;
              }
  
              static class Debug{
                  //change to System.getProperty("ONLINE_JUDGE")==null; for CodeForces
                  public static final boolean LOCAL = System.getProperty("ONLINE_JUDGE")==null;
  
                  
  
                  private static <T> String ts(T t) {
                      if(t==null) {
                          return "null";
                      }
                      try {
                          return ts((Iterable) t);
                      }catch(ClassCastException e) {
                          if(t instanceof int[]) {
                              String s = Arrays.toString((int[]) t);
                              return "{"+s.substring(1, s.length()-1)+"}\n";
                          }else if(t instanceof long[]) {
                              String s = Arrays.toString((long[]) t);
                              return "{"+s.substring(1, s.length()-1)+"}\n";
                          }else if(t instanceof char[]) {
                              String s = Arrays.toString((char[]) t);
                              return "{"+s.substring(1, s.length()-1)+"}\n";
                          }else if(t instanceof double[]) {
                              String s = Arrays.toString((double[]) t);
                              return "{"+s.substring(1, s.length()-1)+"}\n";
                          }else if(t instanceof boolean[]) {
                              String s = Arrays.toString((boolean[]) t);
                              return "{"+s.substring(1, s.length()-1)+"}\n";
                          }
                          try {
                              return ts((Object[]) t);
                          }catch(ClassCastException e1) {
                              return t.toString();
                          }
                      }
                  }
                  private static <T> String ts(T[] arr) {
                      StringBuilder ret = new StringBuilder();
                      ret.append("{");
                      boolean first = true;
                      for(T t: arr) {
                          if(!first) {
                              ret.append(", ");
                          }
                          first = false;
                          ret.append(ts(t));
                      }
                      ret.append("}");
                      return ret.toString();
                  }
                  private static <T> String ts(Iterable<T> iter) {
                      StringBuilder ret = new StringBuilder();
                      ret.append("{");
                      boolean first = true;
                      for(T t: iter) {
                          if(!first) {
                              ret.append(", ");
                          }
                          first = false;
                          ret.append(ts(t));
                      }
                      ret.append("}");
                      return ret.toString();
                  }
                  public static void dbg(PrintStream ps,Object... o) throws Exception {
                      if(LOCAL) {
                          System.setErr(ps);
                          System.err.print("Line #"+Thread.currentThread().getStackTrace()[2].getLineNumber()+": [");
                          for(int i = 0; i<o.length; i++) {
                              if(i!=0) {
                                  System.err.print(", ");
                              }
                              System.err.print(ts(o[i]));
                          }
                          System.err.println("]");
                      }
                  }
              }
  
      }