#include <bits/stdc++.h>
using namespace std;
struct Fast {
    Fast() {
        std::cin.tie(0);
        ios::sync_with_stdio(false);
        cout.precision(20);
    }
} fast;

/* define */
#define FOR(I, X, Y) for (long long(I) = (X); (I) < (Y); (I)++)
#define REP(I, X, Y) for (long long(I) = (Y)-1; (I) >= (X); (I)--)
#define ALL(X) (X).begin(), (X).end()
#define pb push_back
#define COUNT(V, X)                           \
    (upper_bound((V).begin(), (V).end(), X) - \
     lower_bound((V).begin(), (V).end(), X))
#define debug(x) cerr << #x << ':' << x << endl;
#define DEBUG(v)                             \
    {                                        \
        cerr << #v << ':';                   \
        for (auto xv : v) cerr << xv << ' '; \
        cerr << endl;                        \
    }
#define Yes(X) cout << (X ? "Yes" : "No") << endl;
#define YES(X) cout << (X ? "YES" : "NO") << endl;
#define ctoi(C) (C - '0')
#define pow2(x) ((long long)((long long)1 << x))

/* alias */
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<long long>;
using vll = vector<vector<long long>>;
using pi = pair<int, int>;
using pl = pair<long long, long long>;
template <typename T>
using PQ = priority_queue<T>;
template <typename T>
using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const long long dx[] = {1, 0, -1, 0};
const long long dy[] = {0, 1, 0, -1};
const long long dx8[] = {1, 1, 0, -1, -1, -1, 0, 1};
const long long dy8[] = {0, 1, 1, 1, 0, -1, -1, -1};
const long long dx9[] = {1, 1, 0, -1, -1, -1, 0, 1, 0};
const long long dy9[] = {0, 1, 1, 1, 0, -1, -1, -1, 0};
const int INF = 1000000007;
const long long LINF = 1000000000000000007;

/* func */
template <typename T1, typename T2>
inline bool chmin(T1 &a, const T2 &b) {
    if (a > b) a = b;
    return a > b;
}
template <typename T1, typename T2>
inline bool chmax(T1 &a, const T2 &b) {
    if (a < b) a = b;
    return a < b;
}
long long max(long long x, int y) {
    return max(x, (long long)y);
}
long long max(int x, long long y) {
    return max((long long)x, y);
}
long long min(long long x, int y) {
    return min(x, (long long)y);
}
long long min(int x, long long y) {
    return min((long long)x, y);
}

/* library */

/* main */

ll index(const int &x, const int &y) {
    assert(x != y);
    return max(x, y) * 1000 + min(x, y);
}

signed main() {
    ll N;
    cin >> N;
    int in[1000000] = {};
    vector<vector<int>> adj(1000000);
    FOR(i, 0, N) {
        vl A(N - 1);
        FOR(j, 0, N - 1) {
            cin >> A[j];
            A[j]--;
            if (j) {
                adj[index(i, A[j - 1])].push_back(index(i, A[j]));
                in[index(i, A[j])] += 1;
            }
        }
    }
    int dfs[1000000] = {};
    queue<int> que;
    FOR(i, 0, N) {
        FOR(j, i + 1, N) {
            if (in[index(i, j)] == 0) {
                que.push(index(i, j));
                dfs[index(i, j)] = 1;
            }
        }
    }
    while (que.size()) {
        int now = que.front();
        que.pop();
        for (auto to : adj[now]) {
            if (dfs[to] == 0) {
                in[to]--;
                if (in[to] == 0) {
                    que.push(to);
                    dfs[to] = dfs[now] + 1;
                }
            }
        }
    }
    FOR(i, 0, N) {
        FOR(j, i + 1, N) {
            if (dfs[index(i, j)] == 0) {
                cout << -1 << endl;
                return 0;
            }
        }
    }
    cout << *max_element(dfs, dfs + 1000000) << endl;
}

Measured memory_bytes: 47104