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.util.*;
  import java.io.*;
  
  public class C {
      static StringBuilder sb;
      static long fact[];
      static int mod = (int) (1e9 + 7);
      static int[] arr = { 0, 1, 11, 111, 1111, 11111, 111111, 1111111, 11111111, 111111111, 1111111111 };
  
      static ArrayList<Integer> kahnAlgo(ArrayList<Integer>[] graph, int N) {
          LinkedList<Integer> que = new LinkedList<>();
          int[] indegree = new int[N + 1];
  
          for (int i = 1; i <= N; i++) {
              for (int v : graph[i]) {
                  indegree[v]++;
              }
          }
  
          for (int i = 1; i <= N; i++) {
              if (indegree[i] == 0)
                  que.addLast(i);
          }
  
          ArrayList<Integer> topOrder = new ArrayList<>();
          while (que.size() > 0) {
              int rn = que.removeFirst();
              for (int ele : graph[rn]) {
                  indegree[ele]--;
                  if (indegree[ele] == 0)
                      que.add(ele);
              }
              topOrder.add(rn);
  
          }
  
          Collections.reverse(topOrder);
  
          if (topOrder.size() == N)
              return topOrder;
  
          else
              return new ArrayList<>();
  
      }
  
      static int solve(ArrayList<Integer>[] graph, int N) {
          ArrayList<Integer> topOrder = kahnAlgo(graph, N);
  
          // System.out.println(topOrder);
          if (topOrder.size() != N)
              return -1;
  
          HashMap<Integer, Integer> mp = new HashMap<>();
          int maxR = 1;
  
          for (int ele : topOrder) {
              int depSmaller = -1;
              int depGreater = -1;
              for (int v : graph[ele]) {
                  if (v < ele) {
                      depSmaller = Math.max(depSmaller, mp.get(v));
                  } else {
                      depGreater = Math.max(depGreater, mp.get(v));
                  }
              }
  
              int currR = Math.max(depSmaller, depGreater + 1);
              if (currR == 0) {
                  mp.put(ele, 1);
              } else {
                  mp.put(ele, currR);
              }
              maxR = Math.max(currR, maxR);
          }
  
          return maxR;
      }
  
      public static void main(String[] args) {
          sb = new StringBuilder();
          int test = i();
          while (test-- > 0) {
              int N = i();
  
              @SuppressWarnings("unchecked")
              ArrayList<Integer>[] graph = new ArrayList[N + 1];
              for (int i = 1; i <= N; i++) {
                  graph[i] = new ArrayList<>();
  
              }
  
              for (int i = 1; i <= N; i++) {
                  int k = i();
                  while (k-- > 0) {
                      int v = i();
                      graph[i].add(v);
                  }
              }
  
              // System.out.println(Arrays.toString(graph));
  
              int ans = solve(graph, N);
              sb.append(ans + "\n");
  
          }
          System.out.println(sb);
  
      }
  
      /*
       * fact=new long[(int)1e6+10]; fact[0]=fact[1]=1; for(int i=2;i<fact.length;i++)
       * { fact[i]=((long)(i%mod)1L(long)(fact[i-1]%mod))%mod; }
       */
      // **************NCR%P******************
  
      static long p(long x, long y)// POWER FXN //
      {
          if (y == 0)
              return 1;
  
          long res = 1;
          while (y > 0) {
              if (y % 2 == 1) {
                  res = (res * x) % mod;
                  y--;
              }
  
              x = (x * x) % mod;
              y = y / 2;
  
          }
          return res;
      }
  
      static long ncr(int n, int r) {
          if (r > n)
              return (long) 0;
  
          long res = fact[n] % mod;
          // System.out.println(res);
          res = ((long) (res % mod) * (long) (p(fact[r], mod - 2) % mod)) % mod;
          res = ((long) (res % mod) * (long) (p(fact[n - r], mod - 2) % mod)) % mod;
          // System.out.println(res);
          return res;
  
      }
  
      // **************END******************
  
      // *************Disjoint set
      // union*********//
  
      // ***************PRIME FACTORIZE
      // ***********************************//
      static TreeMap<Integer, Integer> prime(long n) {
          TreeMap<Integer, Integer> h = new TreeMap<>();
          long num = n;
          for (int i = 2; i <= Math.sqrt(num); i++) {
              if (n % i == 0) {
                  int nt = 0;
                  while (n % i == 0) {
                      n = n / i;
                      nt++;
                  }
                  h.put(i, nt);
              }
          }
          if (n != 1)
              h.put((int) n, 1);
          return h;
  
      }
  
      // *****CLASS PAIR
      // *************************************************
      static class Pair implements Comparable<Pair> {
          int x;
          long y;
  
          Pair(int x, long y) {
              this.x = x;
              this.y = y;
          }
  
          public int compareTo(Pair o) {
              return (int) (this.y - o.y);
  
          }
  
      }
      // *****CLASS PAIR
      // ***************************************************
  
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private SpaceCharFilter filter;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          public int read() {
              if (numChars == -1)
                  throw new InputMismatchException();
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
  
          public int Int() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              int res = 0;
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
  
          public String String() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              StringBuilder res = new StringBuilder();
              do {
                  res.appendCodePoint(c);
                  c = read();
              } while (!isSpaceChar(c));
              return res.toString();
          }
  
          public boolean isSpaceChar(int c) {
              if (filter != null)
                  return filter.isSpaceChar(c);
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          public String next() {
              return String();
          }
  
          public interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
          }
      }
  
      static class OutputWriter {
          private final PrintWriter writer;
  
          public OutputWriter(OutputStream outputStream) {
              writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
          }
  
          public OutputWriter(Writer writer) {
              this.writer = new PrintWriter(writer);
          }
  
          public void print(Object... objects) {
              for (int i = 0; i < objects.length; i++) {
                  if (i != 0)
                      writer.print(' ');
                  writer.print(objects[i]);
              }
          }
  
          public void printLine(Object... objects) {
              print(objects);
              writer.println();
          }
  
          public void close() {
              writer.close();
          }
  
          public void flush() {
              writer.flush();
          }
      }
  
      static InputReader in = new InputReader(System.in);
      static OutputWriter out = new OutputWriter(System.out);
  
      public static long[] sortlong(long[] a2) {
          int n = a2.length;
          ArrayList<Long> l = new ArrayList<>();
          for (long i : a2)
              l.add(i);
          Collections.sort(l);
          for (int i = 0; i < l.size(); i++)
              a2[i] = l.get(i);
          return a2;
      }
  
      public static int[] sortint(int[] a2) {
          int n = a2.length;
          ArrayList<Integer> l = new ArrayList<>();
          for (int i : a2)
              l.add(i);
          Collections.sort(l);
          for (int i = 0; i < l.size(); i++)
              a2[i] = l.get(i);
          return a2;
      }
  
      public static long pow(long x, long y) {
          long res = 1;
          while (y > 0) {
              if (y % 2 != 0) {
                  res = (res * x);// % modulus;
                  y--;
  
              }
              x = (x * x);// % modulus;
              y = y / 2;
          }
          return res;
      }
  
      // GCD___+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
      public static long gcd(long x, long y) {
          if (x == 0)
              return y;
          else
              return gcd(y % x, x);
      }
      // ******LOWEST COMMON MULTIPLE
      // *********************************************
  
      public static long lcm(long x, long y) {
          return (x * (y / gcd(x, y)));
      }
  
      // INPUT
      // PATTERN********************************************************
      public static int i() {
          return in.Int();
      }
  
      public static long l() {
          String s = in.String();
          return Long.parseLong(s);
      }
  
      public static String s() {
          return in.String();
      }
  
      public static int[] readArray(int n) {
          int A[] = new int[n];
          for (int i = 0; i < n; i++) {
              A[i] = i();
          }
          return A;
      }
  
      public static long[] readArray(long n) {
          long A[] = new long[(int) n];
          for (int i = 0; i < n; i++) {
              A[i] = l();
          }
          return A;
      }
  
  }