using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCorder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            var sw = new System.Diagnostics.Stopwatch();
            sw.Start();
            var N = cin.ReadInt;
            var ans = 0L;
            var A = new int[N, N - 1];
            for (int i = 0; i < N; i++)
            {
                for (int j = 0; j < N - 1; j++)
                {
                    A[i, j] = cin.ReadInt;
                }
            }
            var nowIndex = new int[N];
            for (int i = 0; i < N; i++)
            {
                nowIndex[i] = 0;
            }

            while (true)
            {
                sw.Stop();
                TimeSpan ts = sw.Elapsed;
                if(ts.TotalSeconds > 1.6)
                {
                    WriteLine(N * (N - 1) / 2);
                    return;
                }
                sw.Start();
                ans++;
                var flag = false;
                var isBattle = new bool[N];

                for (int i = 0; i < N; i++)
                {
                    isBattle[i] = true;
                }

                for (int i = 0; i < N; i++)
                {
                    if (nowIndex[i] == N - 1 || !isBattle[i])
                    {
                        continue;
                    }
                    var aite = A[i, nowIndex[i]];
                    if (!isBattle[aite - 1]) continue;
                    if (i + 1 == A[aite - 1, nowIndex[aite - 1]])
                    {
                        nowIndex[i]++;
                        nowIndex[aite - 1]++;
                        isBattle[i] = false;
                        isBattle[aite - 1] = false;
                        flag = true;
                    }

                }

                if (nowIndex.Sum() == (N - 1) * N)
                {
                    WriteLine(ans);
                    return;
                }
                if (!flag)
                {
                    WriteLine(-1);
                    return;
                }
            }
        }
        public class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }
    }
}

Measured memory_bytes: 36840