using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    private int N;

    private int[][] A;

    List<int>[] Path;

    private bool[] B;

    private int Ans = 0;
    private int Cnt = 1;

    private int[] Memo;

    public void Solve()
    {
        var sc = new Scanner();
        N = sc.NextInt();
        A = new int[N][];
        for (int i = 0; i < N; i++)
        {
            A[i] = new int[N - 1];
            for (int j = 0; j < N - 1; j++)
            {
                A[i][j] = sc.NextInt() - 1;
            }
        }

        Path = new List<int>[N * N];
        for (int i = 0; i < N * N; i++)
        {
            Path[i] = new List<int>();
        }

        for (int i = 0; i < N; i++)
        {
            for (int j = 1; j < N - 1; j++)
            {
                Path[Convert(i, A[i][j - 1])].Add(Convert(i, A[i][j]));
            }
        }

        B = new bool[N * N];
        Memo = new int[N * N];
        for (int i = 0; i < N * N; i++)
        {
            Memo[i] = -1;
        }
        
        for (int i = 0; i < N; i++)
        {
            int o;
            if (!Search(Convert(i, A[i][0]), out o))
            {
                Console.WriteLine(-1);
                return;
            }
            
        }

        Console.WriteLine(Memo.Max());
    }

    private bool Search(int i, out int len)
    {
        if (B[i])
        {
            len = -1;
            return false;
        }

        if (Memo[i] != -1)
        {
            len = Memo[i];
            return true;
        }

        B[i] = true;
        len = 0;
        foreach (int i1 in Path[i])
        {
            int o;
            if (!Search(i1, out o))
            {
                len = -1;
                return false;
            }

            len = Math.Max(len, o);
        }

        B[i] = false;
        len++;
        Memo[i] = len;
        return true;
    }

    private int Convert(int i, int j)
    {
        if (i > j)
        {
            int t = i;
            i = j;
            j = t;
        }

        return i * N + j;
    }

    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}

Measured memory_bytes: 99384