import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

public class Main {
  private static void solve() {
    int n = ni();
    int[][] a = ntable(n, n - 1);
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n - 1; j++) {
        a[i][j]--;
      }
    }
    Map<Integer, Integer> map = new HashMap<>();
    int inf = 10000;
    int ptr = 0;
    for (int i = 0; i < n; i++) {
      for (int j = i + 1; j < n; j++) {
        map.put(i * inf + j, ptr);
        map.put(j * inf + i, ptr);
        ptr++;
      }
    }

    int[][] e = new int[n][n - 1];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n - 1; j++) {
        e[i][j] = map.get(i * inf + a[i][j]);
      }
    }

    int m = ptr;
    int[] from = new int[m * 2];
    int[] to = new int[m * 2];

    ptr = 0;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n - 2; j++) {
        from[ptr] = e[i][j];
        to[ptr] = e[i][j + 1];
        ptr++;
      }
    }
    from = Arrays.copyOf(from, ptr);
    to = Arrays.copyOf(to, ptr);
    int[][] g = packD(m, from, to);

    int[] v = sortTopologically(g);
    if (v == null) {
      System.out.println(-1);
      return;
    }

    int[] dp = new int[m];
    for (int i : v) {
      for (int nex : g[i]) {
        dp[nex] = Math.max(dp[nex], dp[i] + 1);
      }
    }

    System.out.println(Arrays.stream(dp).max().getAsInt() + 1);

  }

  public static int[] sortTopologically(int[][] g) {
    int n = g.length;
    int[] ec = new int[n];
    for (int i = 0; i < n; i++) {
      for (int to : g[i])
        ec[to]++;
    }
    int[] ret = new int[n];
    int q = 0;

    // sources
    for (int i = 0; i < n; i++) {
      if (ec[i] == 0)
        ret[q++] = i;
    }

    for (int p = 0; p < q; p++) {
      for (int to : g[ret[p]]) {
        if (--ec[to] == 0)
          ret[q++] = to;
      }
    }
    // loop
    for (int i = 0; i < n; i++) {
      if (ec[i] > 0)
        return null;
    }
    return ret;
  }

  static int[][] packD(int n, int[] from, int[] to) {
    int[][] g = new int[n][];
    int[] p = new int[n];
    for (int f : from)
      p[f]++;
    for (int i = 0; i < n; i++)
      g[i] = new int[p[i]];
    for (int i = 0; i < from.length; i++) {
      g[from[i]][--p[from[i]]] = to[i];
    }
    return g;
  }

  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}


Measured memory_bytes: 186960