/*input
3
2 3
3 1
1 2
*/
/**
    Author: Kristopher Paul
    Date Created: 01-09-2019
    Contest Name:
                _/    _/   _/_/_/_/   _/   _/_/_/_/
               _/  _/     _/    _/   _/   _/
              _/_/       _/_/_/_/   _/   _/_/_/_/
             _/  _/     _/  _/     _/         _/
            _/    _/   _/    _/   _/   _/_/_/_/
**/
#include<bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define int ll
#define pb push_back
#define INF 1e18
#define MOD 1000000007
#define mp make_pair
const double PI=3.141592653589793238462643383279502884197169399375105820974944;
#define REP(i,n) for (int i = 0; i < n; i++)
#define FOR(i,a,b) for (int i = a; i < b; i++)
#define REPD(i,n) for (int i = n-1; i >= 0; i--)
#define FORD(i,a,b) for (int i = a; i >= b; i--)
#define remax(a,b) a = max(a,b)
#define remin(a,b) a = min(a,b)
#define umap unordered_map
#define pii pair<int,int>
#define F first
#define S second
#define mii map<int,int>
#define vi vector<int>
#define vvi vector<vi>
#define itr :: iterator it
#define all(v) v.begin(),v.end()
#define WL(t) while(t--)
#define gcd(a,b) __gcd((a),(b))
#define lcm(a,b) ((a)*(b))/gcd((a),(b))
#define out(x) cout << #x << " is " << x << endl
#define FastIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
using namespace std;
//using namespace __gnu_pbds;

//typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> pbds; // set
//typedef tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update> pbds; // multiset

int ModExp(int x,int y,int m){
    int res = 1;
    x = x % m;
    while (y > 0)
    {
        if (y & 1)
            res = (res*x) % m;

        y = y>>1;
        x = (x*x) % m;
    }
    return res;
}

void solve(){
    int n;
    cin >> n;
    int a[n+1][n];
    FOR(i,1,n+1){
        FOR(j,1,n){
            cin >> a[i][j];
        }
    }
    int tmp[n+1];
    FOR(i,1,n+1){
        tmp[i] = a[i][1];
    }
    int col[n+1];
    FOR(i,1,n+1){
        col[i] = 1;
    }
    int ans = 0;
    while(1){
        bool can = false;
        FOR(i,1,n+1){
            if(tmp[i] != -1 && tmp[tmp[i]] == i){
                can = true;
                break;
            }
        }
        bool ou = true;
        FOR(i,1,n+1){
            if(tmp[i] != -1){
                ou = false;
                break;
            }
        }
        if(ou){
            break;
        }
        if(!can){
            cout << "-1" << endl;
            return;
        }
        bool dead[n+1] = {};
        FOR(i,1,n+1){
            if(!dead[i] && tmp[i] != -1 && !dead[tmp[i]] && tmp[tmp[i]] == i){
                dead[i] = true;
                int j = tmp[i];
                dead[j] = true;
                col[i]++;
                if(col[i] != (n)){
                    tmp[i] = a[i][col[i]];
                }else{
                    tmp[i] = -1;
                }
                col[j]++;
                if(col[j] != (n)){
                    tmp[j] = a[j][col[j]];
                }else{
                    tmp[j] = -1;
                }
            }
        }
        ans++;
    }
    cout << ans << endl;
}

signed main(){
    FastIO;
    int t = 1;
//    cin >> t;
    WL(t){
        solve();
    }
}


Measured memory_bytes: 8064