using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Numerics;

internal partial class Solver {
    public void Run() {
        var n = ni();
        var 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] = ni() - 1;
            }
        }
        var toId = new int[n, n];
        int id = 0;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                toId[i, j] = toId[j, i] = id++;
            }
        }
        var adj = Enumerable.Range(0, id).Select(_ => new List<int>()).ToArray();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n - 2; j++) {
                var t1 = A[i][j];
                var t2 = A[i][j + 1];
                adj[toId[i, t1]].Add(toId[i, t2]);
            }
        }

        cout.WriteLine(MaxDAGDepth(adj));
    }

    static private int MaxDAGDepth(List<int>[] adj) {
        var n = adj.Length;
        var inDegree = new int[n];
        for (int i = 0; i < n; i++) {
            foreach (var p in adj[i]) {
                inDegree[p]++;
            }
        }
        var qu = new Queue<int>();
        for (int i = 0; i < n; i++) {
            if (inDegree[i] == 0) {
                qu.Enqueue(i);
                qu.Enqueue(1);
            }
        }
        int maxDay = 0;
        while (qu.Count > 0) {
            var current = qu.Dequeue();
            var day = qu.Dequeue();
            maxDay = Math.Max(day, maxDay);
            foreach (var next in adj[current]) {
                inDegree[next]--;
                if (inDegree[next] == 0) {
                    qu.Enqueue(next);
                    qu.Enqueue(day + 1);
                }
            }
        }
        if (inDegree.Any(d => d > 0)) return -1;
        return maxDay;
    }

}

// PREWRITEN CODE BEGINS FROM HERE
internal partial class Solver : Scanner {
    public static void Main(string[] args) {
#if LOCAL
        new Solver(Console.In, Console.Out).Run();
#else
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Solver(Console.In, Console.Out).Run();
        Console.Out.Flush();
#endif
    }

    public void RunMulti() {
        while (HasNext()) {
            Run();
        }
    }

#pragma warning disable IDE0052
    private readonly TextReader cin;
    private readonly TextWriter cout;
#pragma warning restore IDE0052

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        cin = reader;
        cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

#pragma warning disable IDE1006
#pragma warning disable IDE0051
    private int ni() { return NextInt(); }
    private int[] ni(int n) { return NextIntArray(n); }
    private long nl() { return NextLong(); }
    private long[] nl(int n) { return NextLongArray(n); }
    private double nd() { return NextDouble(); }
    private double[] nd(int n) { return NextDoubleArray(n); }
    private string ns() { return Next(); }
    private string[] ns(int n) { return NextArray(n); }
#pragma warning restore IDE1006
#pragma warning restore IDE0051
}

public static class LinqPadExtension {
    public static T Dump<T>(this T obj) {
#if LOCAL
        return LINQPad.Extensions.Dump(obj);
#else
        return obj;
#endif
    }
}
public class Scanner {
    private readonly TextReader Reader;
    private readonly Queue<string> TokenQueue = new Queue<string>();
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        Reader = reader;
    }

    public int NextInt() { return int.Parse(Next(), ci); }
    public long NextLong() { return long.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        var array = new string[size];
        for (var i = 0; i < size; i++) {
            array[i] = Next();
        }

        return array;
    }
    public int[] NextIntArray(int size) {
        var array = new int[size];
        for (var i = 0; i < size; i++) {
            array[i] = NextInt();
        }

        return array;
    }

    public long[] NextLongArray(int size) {
        var array = new long[size];
        for (var i = 0; i < size; i++) {
            array[i] = NextLong();
        }

        return array;
    }

    public double[] NextDoubleArray(int size) {
        var array = new double[size];
        for (var i = 0; i < size; i++) {
            array[i] = NextDouble();
        }

        return array;
    }

    public string Next() {
        if (TokenQueue.Count == 0) {
            if (!StockTokens()) {
                throw new InvalidOperationException();
            }
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext() {
        if (TokenQueue.Count > 0) {
            return true;
        }

        return StockTokens();
    }

    private static readonly char[] _separator = new[] { ' ', '\t' };
    private bool StockTokens() {
        while (true) {
            var line = Reader.ReadLine();
            if (line == null) {
                return false;
            }

            var tokens = line.Split(_separator, StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) {
                continue;
            }

            foreach (var token in tokens) {
                TokenQueue.Enqueue(token);
            }

            return true;
        }
    }
}


Measured memory_bytes: 84060