using System;
using static System.Console;
using static System.Math;
using System.IO;
using System.Collections.Generic;
namespace I_am_the_green_coder{
    
    class Inonoa{
        static bool[,] moumita;
        static long[,] maxlens;
        static List<long[]>[,] sakis;
        static long ans = 1;
        static void Main(){
            long n = ILongs()[0];
            long[][] a = ILongLongs(n);
            moumita = new bool[n,n];
            sakis = new List<long[]>[n,n];
            maxlens = new long[n,n];
            
            for(int i=0;i<n;i++){
                for(int j=0;j<n;j++){
                    sakis[i,j] = new List<long[]>();
                    maxlens[i,j] = -1;
                }
            }

            for(int i=0;i<n;i++){
                for(int j=0;j<n-2;j++){
                    sakis[Min(i,a[i][j]-1),Max(i,a[i][j]-1)].Add(new long[2]{Min(i,a[i][j+1]-1),Max(i,a[i][j+1]-1)});
                    //WriteLine("{0},{1}を追加",Min(i,a[i][j+1]-1),Max(i,a[i][j+1]-1));
                }
            }

            for(int i=0;i<n;i++){
                sakis[0,0].Add(new long[2]{Min(i,a[i][0]-1),Max(i,a[i][0]-1)});
            }
            
            long an = Dfs(0,0) - 1;
            if(an>=n*n)WriteLine(-1);
            else WriteLine(an);

        }

        static long Dfs(long x, long y){
            //1つ先の試合群のdfsの値のmaxに1足してreturn
            //試合群それぞれの計算結果はメモする
            //閉路も考慮せよ
            
            //WriteLine("{0},{1}",x,y);
            
            moumita[x,y] = true;
            long ans = 1;
            
            foreach(long[] saki in sakis[x,y]){
                if(moumita[saki[0],saki[1]])return moumita.Length*2;
                if(maxlens[saki[0],saki[1]]>0){
                    if(ans<=maxlens[saki[0],saki[1]])ans = maxlens[saki[0],saki[1]] + 1;
                }else{
                    long sakidfs = Dfs(saki[0],saki[1]);
                    if(ans<=sakidfs)ans = sakidfs + 1;
                }
            }
            
            maxlens[x,y] = ans;
            
            moumita[x,y] = false;
            
            return ans;
        }

        static readonly long MOD = 1000000007;

        ///<summary>a_1, a_2, a_3, ...みたいなの</summary>
        static long[] ILongs(){
            string[] s = ReadLine().Split();
            long[] re = new long[s.Length];
            for(long i=0;i<s.Length;i++){
                re[i] = long.Parse(s[i]);
            }
            return re;
        }

        ///<summary>xooxoxoxxoxo...みたいなの</summary>
        static char[] IChars(){
            return ReadLine().ToCharArray();
        }

        ///<summary>n m とかをちょっとはやくかくだけ</summary>
        static string[] IStrings(){
            return ReadLine().Split();
        }

        ///<summary>n行の入力を取ったり</summary>
        static long[][] ILongLongs(long n){
            long[][] re = new long[n][];
            for(long i=0;i<n;i++){
                string[] s = ReadLine().Split();
                re[i] = new long[s.Length];
                for(long j=0;j<s.Length;j++){
                    re[i][j] = long.Parse(s[j]);
                }
            }
            return re;
        }

        ///<summary>n行の文字列を取ったり</summary>
        static char[][] ICharsChars(long n){
            char[][] re = new char[n][];
            for(long i=0;i<n;i++){
                re[i] = ReadLine().ToCharArray();
            }
            return re;
        }
    }
}


Measured memory_bytes: 183244