#include <vector>
#include <iostream>
#include <cmath>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <fstream>
#include <unistd.h>
#include <string.h>
#include <string>
#include <numeric>
#include <queue>
#include <deque>
#include <sstream>
#include <iomanip>
#include <set>
#include <stack>
#include <cassert>
#include <functional>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef vector<string> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<vvd> vvvd;
typedef pair<ll, ll> PL;
typedef vector<PL> vpl;
typedef vector<vector<PL>> vvpl;
const int INF = 1001001001;
const ll LINF = 1e17;
const double pi = 3.1415926535897932;
const string endstr = "\n";
#define FOR(i, a, b) for(ll i = (a); i < b; i++)
#define RFOR(i, a, b) for(ll i = (a); i > b; i--)
#define rep(i, n) for(ll i = 0; i < n; i++)
#define rrep(i, n) for(ll i = n-1; i > -1; i--)
#define FORMAP(it, m) for(auto it = m.begin(); it != m.end(); it++)
#define ff first
#define ss second
#define pb push_back
#define epb emplace_back
#define ALL(X) (X).begin(),(X).end()

template <typename T>
T gcd(T a, T b) {
    return (a == 0) ? b : gcd(b%a, a);
}
template <typename T>
T lcm(T a, T b) {
    return a / gcd(a, b) * b;
}

bool p_comp_fs(const PL p1, const PL p2){ return p1.first < p2.first;};
bool p_comp_fg(const PL p1, const PL p2){ return p1.first > p2.first;};
bool p_comp_ss(const PL p1, const PL p2){ return p1.second < p2.second;};
bool p_comp_sg(const PL p1, const PL p2){ return p1.second > p2.second;};
template <typename T>
vector<T> uniquen(vector<T> vec){
    sort(ALL(vec));
    vec.erase(unique(vec.begin(), vec.end()), vec.end());
    return vec;
}

inline ll popcnt(ll x){return __builtin_popcountll((unsigned long long)x);};
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
//friend bool operator<(const stc& lhs, const stc& rhs){
//    return std::tie(lhs.l, lhs.r) < std::tie(rhs.l, rhs.r);
//}



int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N; cin >> N;
    vector<queue<ll>> vq(N);
    rep(i, N){
        rep(_, N-1){
            ll a; cin >> a; a--; vq[i].push(a);
        }
    }
    
    vvb used(N, vb(N, false));
    priority_queue<pair<ll, PL>, vector<pair<ll, PL>>, greater<pair<ll, PL>>> pq;
    vl d(N, 0);
    rep(i, N){
        ll a = vq[i].front(); vq[i].pop();
        used[i][a] = true;
        if(used[a][i]){
            ll mx = max(d[a], d[i]);
            pq.push({mx+1, {a, i}});
            d[a] = mx+1; d[i] = mx+1;
        }
    }
    
    while (!pq.empty()) {
        PL p = pq.top().ss; pq.pop();
        auto& vf = vq[p.ff];
        auto& vs = vq[p.ss];
        if(!vf.empty()){
            ll fto = vf.front(); vf.pop();
            used[p.ff][fto] = true;
            if(used[fto][p.ff]){
                ll mx = max(d[p.ff], d[fto]);
                pq.push({mx+1, {p.ff, fto}});
                d[p.ff] = mx+1; d[fto] = mx+1;
            }
        }

        if(!vs.empty()){
            ll sto = vs.front(); vs.pop();
            used[p.ss][sto] = true;
            if(used[sto][p.ss]){
                ll mx = max(d[p.ss], d[sto]);
                pq.push({mx+1, {p.ss, sto}});
                d[p.ss] = mx+1; d[sto] = mx+1;
            }
        }
    }
    
    bool ok = true;
    rep(i, N) rep(j, N) if(i!=j){
        if(!used[i][j]){
            ok = false; i = N; j = N; break;
        }
    }
    if(ok){
        ll ans = 0;
        rep(i, N) chmax(ans, d[i]);
        cout << ans << endstr;
    }
    else{
        cout << -1 << endstr;
    }
    return 0;
}


Measured memory_bytes: 9216