#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_of_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/

int max_len;
struct DirectedGraph
{
    int V; // 頂点数
    vector<vector<int> > to;
    vector<vector<int> > from;

    vector<bool> used;
    vector<int> vs;
    vector<int> depth;

    void dfs(int v)
    {
        used[v] = true;
        for (auto t : to[v]) if (!used[t]) dfs(t);
        vs.push_back(v);
    }
    int rdfs(int v, int k)
    {
        int ret = 0;
        used[v] = true;
        cmp[v] = k;
        for (auto t : from[v])
        {
            if (!used[t])
                 rdfs(t, k);
            mmax(depth[v], depth[t] + 1);
        }
        return ret + 1;
    }

    vector<int> cmp;
    DirectedGraph(int V) : V(V),
                           to(vector<vector<int> >(V)), 
                           from(vector<vector<int> >(V)),
                           cmp(vector<int>(V)),
                           depth(vector<int>(V))
                           {}
    void add_edge(int from_, int to_)
    {
        to[from_].push_back(to_);
        from[to_].push_back(from_);
    }

    int scc_num = -1;
    int scc()
    {
        used = vector<bool>(V, false);
        vs.clear();
        for (int v = 0; v < V; v++) if (!used[v]) dfs(v);

        used = vector<bool>(V, false);
        scc_num = 0;
        for (int i = vs.size() - 1; i >= 0; i--) if (!used[vs[i]])
        {
            mmax(max_len, rdfs(vs[i], scc_num++));
        }
        return scc_num; // 強連結成分の個数を返却
    }

    // scc()を実行したあと，強連結成分を潰したトポロジカル順序のグラフを生成
    DirectedGraph generateTopologicalGraph()
    {
        DirectedGraph newgraph(scc_num);
        REP(s, V) for (auto t : to[s])
        {
            if (cmp[s] != cmp[t]) newgraph.add_edge(cmp[s], cmp[t]);
        }
        return newgraph;
    }
};

int main()
{
    int N;
    cin >> N;
    DirectedGraph g((N + 1) * (N + 1));

    FOR(i, 1, N + 1)
    {
        vector<int> a(N - 1);
        cin >> a;
        REP(j, N - 1) a[j] = min(i, a[j]) * N + max(i, a[j]);
        REP(j, N - 2)
        {
            g.add_edge(a[j], a[j + 1]);
        }
    }
    int s = g.scc();
    if (s != (N + 1) * (N + 1))
    {
        puts("-1");
        return 0;
    }

    cout << *max_element(ALL(g.depth)) + 1 << endl;
}


Measured memory_bytes: 92272