#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define SPEED ios_base::sync_with_stdio(false); cin.tie(NULL);
#define FOR(i, a, b) for (ll i = a; i < b; ++i)
#define RFOR(i, b, a) for (ll i = b; i >= a; --i)
#define ALL(x) x.begin(), x.end()
#define DEBUG(args...) { string _s = #args; replace(ALL(_s), ' ', '\0');\
replace(ALL(_s), ',', ' ');\
stringstream _ss(_s); istream_iterator<string> _it(_ss); _debug(_it, args);}
#define endl "\n"
#define F first
#define S second
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)

using namespace std;
using namespace __gnu_pbds;

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

void _debug(istream_iterator<string>) {}
template<typename T, typename... Args>
void _debug(istream_iterator<string> it, T first, Args... args) {
    cerr << ">> " << *it << " : " << first << endl; _debug(++it, args...);
}
template <typename T1, typename T2>
inline ostream& operator << (ostream& out, const pair<T1, T2>& p) {
    return out << "(" << p.F << ", " << p.S << ")";
}
template<typename T>
inline ostream& operator << (ostream& out, const vector<T>& v) {
    if (v.empty()) return out << "[]";
    else { out << '['; for (auto& e : v) { out << e << ", "; } return out << "\b\b]"; }
}
template<typename T>
inline ostream& operator << (ostream& out, const set<T>& s) {
    if (s.empty()) return out << "{}";
    else { out << '{'; for (auto& e : s) { out << e << ", "; } return out << "\b\b}"; }
}
template<typename T>
inline ostream& operator << (ostream& out, const unordered_set<T>& s) {
    return out << set<T>(ALL(s));
}
template<typename T1, typename T2>
inline ostream& operator << (ostream& out, const map<T1, T2>& m) {
    if (m.empty()) return out << "{}";
    out << '{'; for (auto& p : m) { out << p << ", "; } return out << "\b\b}";
}
template<typename T1, typename T2>
inline ostream& operator << (ostream& out, const unordered_map<T1, T2>& m) {
    return out << map<T1, T2>(ALL(m));
}
template<typename T>
inline ostream& operator << (ostream& out, const ordered_set<T>& s) {
    return out << set<T>(ALL(s));
}

typedef long long ll;
typedef long double ld;
typedef vector<long long> vll;
typedef pair<ll, ll> pll;
typedef vector<pair<ll, ll>> vpll;
typedef unordered_map<ll, ll> STll;
/************************************** MAIN PROGRAM ********************************************/

int main()
{
    //freopen("input.txt", "r", stdin);
    SPEED
    ll n;
    cin >> n;
    vector<vector<int>> a(n, vector<int>(n - 1));
    for (auto &v : a) {
        for (auto &e : v) {
            cin >> e;
            e--;
        }
    }
    vector<int> ptrOfPlayer(n);
    vector<int> newGuys;
    FOR(i, 0, n) {
        newGuys.push_back(i);
    }

    int matches = 0;
    int ans = 0;
    map<pair<int, int>, int> voteForMatch;

    while (matches < n * (n - 1) / 2) {
        vector<pair<int, int>> matchesWith2Votes;

        for (auto i : newGuys) {
            int x = i, y = a[i][ptrOfPlayer[i]];
            if (x > y) swap(x, y);
            voteForMatch[{x, y}]++;
            if (voteForMatch[{x, y}] == 2) {
                matchesWith2Votes.push_back({x, y});
            }
        }
        int matchesToday = 0;

        newGuys.clear();
        for (auto p : matchesWith2Votes) {
            int x = p.first, y = p.second;

            ptrOfPlayer[x]++;
            ptrOfPlayer[y]++;

            newGuys.push_back(x);
            newGuys.push_back(y);

            voteForMatch[{x, y}] -= 2;
            matchesToday++;
        }
        matches += matchesToday;
        if (matchesToday == 0) {
            cout << -1;
            return 0;
        }
        ans++;
    }
    cout << ans;
}
/************************************** END OF PROGRAM ******************************************/
/** Stuff you should look for:
 * int overflow, array bounds, over-counting, graph is not a tree/connected
 * special cases (n=1?), set/unordered_set TLE, multi-set/set error
 * do something instead of nothing and stay organized
 */


Measured memory_bytes: 35584