#define DEBUG 1
#include <algorithm>
#include <cmath>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using tll = tuple<ll, ll, ll>;
#define all(v) (v).begin(), (v).end()
#define for1(i, n) for (ll i = 0; i < (n); i++)
#define for2(i, m, n) for (ll i = (m); i < (n); i++)
#define for3(i, m, n, d) for (ll i = (m); i < (n); i += (d))
#define rfor2(i, m, n) for (ll i = (m); i > (n); i--)
#define rfor3(i, m, n, d) for (ll i = (m); i > (n); i += (d))
#define INF 1111111111111111111LL
#define MOD 1000000007LL  // 10**9 + 7
#define print(...) print_1(__VA_ARGS__)
#if DEBUG
#define dump(...) dump_1(#__VA_ARGS__, __VA_ARGS__)
#else
#define dump(...)
#endif
template <typename Head>
void dump_1(const char* str, Head&& h)
{
    cerr << str << ": " << h << '\n';
}
template <typename Head, typename... Tail>
void dump_1(const char* str, Head&& h, Tail&&... t)
{
    while (*str != ',') {
        cerr << *str++;
    }
    cerr << ": " << h << ' ';
    dump_1(str + 1, t...);
}
template <typename T1, typename T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& v)
{
    os << '(' << v.first << ", " << v.second << ')';
    return os;
}
template <typename T1, typename T2, typename T3>
ostream& operator<<(ostream& os, const tuple<T1, T2, T3>& v)
{
    os << '(' << get<0>(v) << ", " << get<1>(v) << ", " << get<2>(v) << ')';
    return os;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    for (auto it = v.begin(); it != v.end(); it++) {
        if (it != v.begin()) {
            os << ' ';
        }
        os << *it;
    }
    return os;
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& v)
{
    for (auto it = v.begin(); it != v.end(); it++) {
        if (it != v.begin()) {
            os << ' ';
        }
        os << *it;
    }
    return os;
}
template <typename T1, typename T2>
ostream& operator<<(ostream& os, const map<T1, T2>& v)
{
    os << '{';
    for (auto it = v.begin(); it != v.end(); it++) {
        if (it != v.begin()) {
            os << ", ";
        }
        os << it->first << ':' << it->second;
    }
    os << '}';
    return os;
}
void Yes(void) { cout << "Yes" << '\n'; }
void No(void) { cout << "No" << '\n'; }
void YES(void) { cout << "YES" << '\n'; }
void NO(void) { cout << "NO" << '\n'; }
template <typename T>
void chmax(T& a, const T& b)
{
    if (a < b) {
        a = b;
    }
}
template <typename T>
void chmin(T& a, const T& b)
{
    if (a > b) {
        a = b;
    }
}
template <typename T>
void vin(vector<T>& v, ll len)
{
    for1 (i, len) {
        cin >> v[i];
    }
}
template <typename Head>
void print_1(Head&& h)
{
    cout << h << '\n';
}
template <typename Head, typename... Tail>
void print_1(Head&& h, Tail&&... t)
{
    cout << h << ' ';
    print_1(t...);
}
//---------------------------------------------------------
ll A[1001][1001];
ll c[2][1001];
void solve()
{
    ll ans = 0;
    ll N;
    cin >> N;
    for1 (h, N) {
        for1 (w, N - 1) {
            ll a;
            cin >> a;
            A[h][w] = a - 1;
        }
    }
    bool loop = true;
    ll t0 = 1;
    ll t1 = 0;
    while (loop) {
        loop = false;
        t0 = 1 - t0;
        t1 = 1 - t1;
        for1 (i, N) {
            if (c[t0][i] == N - 1) continue;
            ll j = A[i][c[t0][i]];
            if (c[t0][j] == N - 1) continue;
            if (A[j][c[t0][j]] == i) {
                c[t1][i] = c[t0][i] + 1;
                c[t1][j] = c[t0][j] + 1;
                loop = true;
            }
        }
        for1 (i, N) {
            chmax(c[t1][i], c[t0][i]);
        }
        if (loop) {
            ans++;
        }
    }
    for1 (i, N) {
        if (c[t1][i] < N - 1) {
            print(-1);
            return;
        }
    }

    print(ans);
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(12);
    cerr << fixed << setprecision(12);
    solve();
}


Measured memory_bytes: 8064