#include <bits/stdc++.h>
using namespace std;
using LL = long long;

#define fs first
#define sc second

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }


// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

// std::vector Initialization
template<typename T>
void fill_all(T& arr, const T& v) { arr = v; }
template<typename T, typename U>
void fill_all(T& arr, const U& v) { for (auto& i : arr) fill_all(i, v); }

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::deque Debug
template<typename T>
ostream& operator<<(ostream& os, const deque<T>& d) {
    os << "[";
    bool a = 1;
    for (auto e : d) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl


struct edge { int to, cost; };
ostream& operator<<(ostream& os, const edge& e) {
    os << "(" << e.to << ", " << e.cost << ")";
    return os;
}

const LL LINF = 1LL<<60;
const int IINF = 1<<30;
const LL MOD = 1e9+7;

bool construct_dag(const auto& G, auto& ord) {
    ord.resize(G.size());

    vector<int> deg(G.size());

    for (int v = 0; v < G.size(); ++v) {
        for (auto u : G[v]) {
            ++deg[u];
        }
    }

    stack<int> st;
    for (int v = 0; v < deg.size(); ++v) {
        if (deg[v] == 0) st.push(v);
    }

    int k = 0;
    while (!st.empty()) {
        int v = st.top(); st.pop();
        ord[k++] = v;
        for (auto u : G[v]) {
            if (--deg[u] == 0) {
                st.push(u);
            }
        }
    }

    return k == G.size();
}

int main()
{
    int n; cin >> n;

    auto a = make_v<int>(n, n-1);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n-1; ++j) {
            cin >> a[i][j]; --a[i][j];
        }
    }

    vector<vector<int>> G(n*n);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n-2; ++j) {
            G[max(i,a[i][j])*n + min(i,a[i][j])].push_back(
                    max(i,a[i][j+1])*n + min(i,a[i][j+1])
                    );
        }
    }

    vector<int> ord;
    if (!construct_dag(G, ord)) {
        cout << -1 << endl;
        return 0;
    }

    vector<int> len(G.size());
    for (int i = G.size()-1; i >= 0; --i) {
        int v = ord[i];

        int ma = 0;
        for (auto u : G[v]) {
            chmax(ma, len[u]);
        }

        len[v] = ma + 1;
    }

    cout << *max_element(len.begin(), len.end()) << endl;

    return 0;
}


Measured memory_bytes: 53120