/**
 * Created at 04:57 on 2019-09-02
 */

import java.io.*;
import java.util.*;

public class Main {

  static FastScanner sc = new FastScanner();
  static Output out = new Output(System.out);

  static final int[] dx = {0, 1, 0, -1};
  static final int[] dy = {-1, 0, 1, 0};

  static final long MOD = (long) (1e9 + 7);
  static final long INF = Long.MAX_VALUE / 2;

  static final int e5 = (int) 1e5;

  public static class Solver {
    public Solver() {

      int N = sc.nextInt();

      int[][] A = new int[N][N-1];

      for (int i=0; i<N; i++) {
        for (int j=0; j<N-1; j++) {
          A[i][j] = sc.nextInt()-1;
        }
      }

      ArrayDeque<Game> queue = new ArrayDeque<Game>();

      int[] count = new int[N];

      for (int i=0; i<N; i++) {
        int opponent = A[i][0];
        if (A[opponent][0] == i) {
          queue.add(new Game(i, opponent));
        }
      }

      queue.add(new Game(-1, -1));

      boolean[][] done = new boolean[N][N];

      long ans = 0;
      while (!queue.isEmpty()) {
        Game game = queue.removeFirst();
        if (game.a == -1) {
          ans++;
          if (queue.isEmpty()) break;
          else {
            queue.add(new Game(-1, -1));
            continue;
          }
        }

        if (done[game.a][game.b] || done[game.b][game.a]) {
          continue;
        }

        done[game.a][game.b] = true;
        count[game.a]++;
        count[game.b]++;

        if (count[game.a] < N-1) {
          int opponentA = A[game.a][count[game.a]];
          if (count[opponentA] < N-1) {
            if (A[opponentA][count[opponentA]] == game.a) {
              queue.add(new Game(game.a, opponentA));
            }
          }
        }
        if (count[game.b] < N-1) {
          int opponentB = A[game.b][count[game.b]];
          if (count[opponentB] < N-1) {
            if (A[opponentB][count[opponentB]] == game.b) {
              queue.add(new Game(game.b, opponentB));
            }
          }
        }

      }

      boolean ok = true;
      for (int i=0; i<N; i++) {
        if (count[i] != N-1) {
          ok = false;
          break;
        }
      }

      out.println(ok ? ans : -1);

    }

    class Game {
      int a, b;
      Game(int A, int B) {
        a = A;
        b = B;
      }
    }
  }

  public static void main(String[] args) {
    new Solver();
    out.flush();
  }

  static class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
      if (ptr < buflen) {
        return true;
      } else {
        ptr = 0;
        try {
          buflen = in.read(buffer);
        } catch (IOException e) {
          e.printStackTrace();
        }
        if (buflen <= 0) {
          return false;
        }
      }
      return true;
    }

    private int readByte() {
      if (hasNextByte()) return buffer[ptr++];
      else return -1;
    }

    private static boolean isPrintableChar(int c) {
      return 33 <= c && c <= 126;
    }

    private void skipUnprintable() {
      while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
    }

    public boolean hasNext() {
      skipUnprintable();
      return hasNextByte();
    }

    public String next() {
      if (!hasNext()) throw new NoSuchElementException();
      StringBuilder sb = new StringBuilder();
      int b = readByte();
      while (isPrintableChar(b)) {
        sb.appendCodePoint(b);
        b = readByte();
      }
      return sb.toString();
    }

    public long nextLong() {
      if (!hasNext()) throw new NoSuchElementException();
      long n = 0;
      boolean minus = false;
      int b = readByte();
      if (b == '-') {
        minus = true;
        b = readByte();
      }
      if (b < '0' || '9' < b) {
        throw new NumberFormatException();
      }
      while (true) {
        if ('0' <= b && b <= '9') {
          n *= 10;
          n += b - '0';
        } else if (b == -1 || !isPrintableChar(b)) {
          return minus ? -n : n;
        } else {
          throw new NumberFormatException();
        }
        b = readByte();
      }
    }

    public int nextInt() {
      return (int) nextLong();
    }

    public int[] nextIntArray(int N, boolean oneBased) {
      if (oneBased) {
        int[] array = new int[N + 1];
        for (int i = 1; i <= N; i++) {
          array[i] = sc.nextInt();
        }
        return array;
      } else {
        int[] array = new int[N];
        for (int i = 0; i < N; i++) {
          array[i] = sc.nextInt();
        }
        return array;
      }
    }

    public long[] nextLongArray(int N, boolean oneBased) {
      if (oneBased) {
        long[] array = new long[N + 1];
        for (int i = 1; i <= N; i++) {
          array[i] = sc.nextLong();
        }
        return array;
      } else {
        long[] array = new long[N];
        for (int i = 0; i < N; i++) {
          array[i] = sc.nextLong();
        }
        return array;
      }
    }
  }

  static class Output extends PrintWriter {

    public Output(PrintStream ps) {
      super(ps);
    }

    public void print(int[] a, String separator) {
      for (int i = 0; i < a.length; i++) {
        if (i == 0) print(a[i]);
        else print(separator + a[i]);
      }
      println();
    }

    public void print(long[] a, String separator) {
      for (int i = 0; i < a.length; i++) {
        if (i == 0) print(a[i]);
        else print(separator + a[i]);
      }
      println();
    }

    public void print(String[] a, String separator) {
      for (int i = 0; i < a.length; i++) {
        if (i == 0) print(a[i]);
        else print(separator + a[i]);
      }
      println();
    }

    public void print(ArrayList a, String separator) {
      for (int i = 0; i < a.size(); i++) {
        if (i == 0) print(a.get(i));
        else print(separator + a.get(i));
      }
      println();
    }
  }

}


Measured memory_bytes: 47760