#include <bits/stdc++.h>
using namespace std;
#define int long long
#define stoi stoll
using pii=pair<int,int>;
using vi = vector<int>;
using vvi = vector<vi>;
#define all(c) begin(c),end(c)
#define rall(c) rbegin(c),rend(c)
#define fore(x,c) for(auto &&x:c)
#define rep(i,a,n) for(int i=a,i##len=(int)(n);i<i##len;++i)
#define rrep(i, a, n) for(int i=(int)(n-1);i>=a;--i)
#define sz(c) ((int)c.size())
#define contains(c,x) (c.find(x)!=end(c))
#define inseg(l,x,r) ((l)<=(x)&&(x)<(r))
#define dump(...)
#define pb push_back
#define _ 0
const signed INF_=1001001001; const long long INF=1001001001001001001LL;
const int DX[9]={0,1,0,-1,1,1,-1,-1,0},DY[9]={-1,0,1,0,-1,1,1,-1,0};
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) {
    for (auto i = begin(v); i != end(v); i++) os<<*i<<(i==end(v)-1?"":" ");return os;}
template<class T> istream& operator>>(istream &is,vector<T> &v) {
    for (auto i = begin(v); i != end(v); i++) is>>*i;return is;}
template<class T,class U> istream& operator>>(istream &is, pair<T,U> &p) {
    is>>p.first>>p.second;return is;}
template<class T, class U> bool chmax(T &a,const U &b){return a<b?a=b,1:0;}
template<class T, class U> bool chmin(T &a,const U &b){return a>b?a=b,1:0;}
template <class T> void psum(T& c) {partial_sum(begin(c), end(c), begin(c));}
template<class T> using heap=priority_queue<T,vector<T>,greater<T>>;
struct before_main_function {
    before_main_function() {
        cin.tie(nullptr); ios::sync_with_stdio(0);
        cout << setprecision(15) << fixed;
        // #define endl "\n"
    }
} before_main_function;
//------------------8<------------------------------------8<--------------------

signed main() {
    int N;
    cin >> N;
    vector<deque<int>> A(N);
    vvi G(N, vi(N, 0));
    rep(i, 0, N) {
        rep(j, 0, N - 1) {
            int x;
            cin >> x;
            x--;
            A[i].push_back(x);
        }
        G[i][A[i].front()] = 1;
        A[i].pop_front();
    }

    vector<pii> cycle;
    int rem = N;

    rep(i, 0, N) {
        rep(j, i + 1, N) {
            if (G[i][j] && G[j][i]) {
                cycle.push_back({i, j});
            }
        }
    }
    rep(loop, 0, N * (N - 1) / 2) {
        dump(loop, cycle);
        // remove cycles
        vector<pii> next_cycle;
        while (sz(cycle)) {
            int x, y;
            tie(x, y) = cycle.back(); cycle.pop_back();
            G[x][y] = G[y][x] = 0;

            if (A[x].empty()) {
                rem--;
            } else {
                int tmp = A[x].front(); A[x].pop_front();
                G[x][tmp] = 1; 
                if (G[x][tmp] && G[tmp][x]) {
                    dump(x, tmp);
                    next_cycle.push_back({x, tmp});
                }
            }

            if (A[y].empty()) {
                rem--;
            } else {
                int tmp = A[y].front(); A[y].pop_front();
                G[y][tmp] = 1; 
                if (G[y][tmp] && G[tmp][y]) {
                    dump(y, tmp);
                    next_cycle.push_back({y, tmp});
                }
            }
        }
        cycle.swap(next_cycle);

        if (rem == 0) {
            cout << loop + 1 << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return (0^_^0);
}



Measured memory_bytes: 16896