#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

typedef tree<int, null_type, less<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define PSET(x,y) fixed<<setprecision(y)<<x
#define pb push_back
#define pf push_front
#define pii pair<int,int>
#define mp make_pair
#define vi vector<int>
#define vip vector<pair<int,int> >
#define ff first
#define ss second
#define int long long
#define SIZE 200010
#define mod 1000000007
#define BIG 998244353
#define s(t) scanf("%d",&t)
#define p(t) printf("%d\n",t)
#define mii map<int,int>
#define MSET(table,i) memset(table, i, sizeof(table))
#define endl '\n'
#define tc int t;cin>>t;while(t--)
#define pi  3.1415926358
#define print(x) for(auto el: x) cout<<el<<" ";cout<<endl
#define bits(x) __builtin_popcount(x)
#define minimum(a,n) min_element(a,a+n)-a
#define maximum(a,n) max_element(a,a+n)-a
#define pqbig priority_queue<int>
#define pqsmall priority_queue<int,vector<int>,greater<int> >
#define all(v) v.begin(),v.end()
#define sitr set<int>:: iterator
#define mitr map<int,int>:: iterator

#define trace1(x)                cerr<<#x<<": "<<x<<endl
#define trace2(x, y)             cerr<<#x<<": "<<x<<" | "<<#y<<": "<<y<<endl
#define trace3(x, y, z)          cerr<<#x<<":" <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<endl
#define trace4(a, b, c, d)       cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<endl
#define trace5(a, b, c, d, e)    cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<endl
#define trace6(a, b, c, d, e, f) cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<" | "<<#f<<": "<<f<<endl

const int N=1e3+5;
int arr[N][N];
int pointers[N];

int32_t main()
{
    fast;
    int n;cin>>n;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n-1;j++)
            cin>>arr[i][j];
    }

    for(int i=1;i<=n;i++)
        pointers[i]=1;

    int iterations=0;

    int days=0;
    int sum=n;
    while(sum!=n*n)
    {
        iterations++;
        bool tmp[N];
        for(int i=1;i<=n;i++)
            tmp[i]=false;
        int cnt=0;
        for(int i=1;i<=n;i++)
        {
            //trace3(i,arr[i][pointers[i]],pointers[i]);
            if(!tmp[i] and !tmp[arr[i][pointers[i]]] and arr[arr[i][pointers[i]]][pointers[arr[i][pointers[i]]]]==i)
            {
                cnt+=2;
                //trace2(i,arr[i][pointers[i]]);
                tmp[i]=true;
                tmp[arr[i][pointers[i]]]=true;
                //trace2(i,arr[i][pointers[i]]);
                pointers[arr[i][pointers[i]]]++;
                pointers[i]++;
                //trace2(pointers[arr[i][pointers[i]]],arr[i][pointers[i]]);
            }
        }
        sum+=cnt;
        days++;

        if(cnt==0)
        {
            cout<<-1;
            return 0;
        }

        if(iterations>5*N)
        {
            cout<<(n*(n-1))/2;
            return 0;
        }

    }
    cout<<days;
}

Measured memory_bytes: 8064