#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdint>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <sys/timeb.h>
#include <vector>

using namespace std;

#define repr(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) repr(i, 0, n)
#define reprrev(i, a, b) for (int i = (int)(b)-1; i >= (int)(a); i--)
#define reprev(i, n) reprrev(i, 0, n)
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define chmin(mi, val) mi = min(mi, val)
#define chmax(ma, val) ma = max(ma, val)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define mp make_pair
#define mt make_tuple
#define INF 1050000000
#define INFR INT_MAX
#define INFL (long long)(4e18)
#define INFLR LLONG_MAX
#define EPS (1e-10)
#define MOD 1000000007
//#define MOD 998244353
#define PI 3.141592653589793238
#define RMAX 4294967295

using vi = vector<int>;
using vvi = vector<vector<int>>;
using vvvi = vector<vector<vector<int>>>;
using vvvvi = vector<vector<vector<vector<int>>>>;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using vvvll = vector<vector<vector<ll>>>;
using vd = vector<double>;
using vvd = vector<vector<double>>;
using vb = vector<bool>;
using vvb = vector<vector<bool>>;
using vc = vector<char>;
using vvc = vector<vector<char>>;
using vs = vector<string>;
using vvs = vector<vector<string>>;
using Pi = pair<int, int>;
using vPi = vector<Pi>;
using vvPi = vector<vector<Pi>>;
using vvvPi = vector<vector<vector<Pi>>>;
using vvvvPi = vector<vector<vector<vector<Pi>>>>;
using Pll = pair<ll, ll>;
using vPll = vector<Pll>;
using Pd = pair<double, double>;
using vPd = vector<Pd>;
template <class T>
using vec = vector<T>;
template <class T>
using pql = priority_queue<T, vector<T>, greater<T>>;
using Comp = complex<double>;

// vvvvvvvvvvvvvvvvvvvvvvv debug output vvvvvvvvvvvvvvvvvvvvvvv
// vector input
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}
// pair
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}
// vector
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
    os << "{";
    for (int i = 0; i < vec.size(); i++) {
        os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
    }
    os << "}";
    return os;
}
// deque
template <typename T>
ostream &operator<<(ostream &os, const deque<T> &vec) {
    os << "{";
    for (int i = 0; i < vec.size(); i++) {
        os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
    }
    os << "}";
    return os;
}
// map
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &map_var) {
    os << "{";
    repi(itr, map_var) {
        os << *itr;
        itr++;
        if (itr != map_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
// set
template <typename T>
ostream &operator<<(ostream &os, const set<T> &set_var) {
    os << "{";
    repi(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
// multiset
template <typename T>
ostream &operator<<(ostream &os, const multiset<T> &set_var) {
    os << "{";
    repi(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}

#define DUMPOUT cerr

void dump_func() {
    DUMPOUT << endl;
}
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) {
        DUMPOUT << ", ";
    }
    dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                            \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]"        \
            << endl                                                            \
            << "    ",                                                         \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

// ^^^^^^^^^^^^^^^^^^^^^^^ debug output ^^^^^^^^^^^^^^^^^^^^^^^

string YN(bool y, int id = 0) {
    if (id) cout << id;
    return (y ? "YES" : "NO");
}
string yn(bool y, int id = 0) {
    if (id) cout << id;
    return (y ? "Yes" : "No");
}
string ON(bool y, int id = 0) {
    if (id) cout << id;
    return (y ? "OK" : "NG");
}

int dir4[4][2] = {{0, -1}, {-1, 0}, {1, 0}, {0, 1}};
int dir8[8][2] = {{-1, -1}, {0, -1}, {1, -1}, {-1, 0},
                  {1, 0},   {-1, 1}, {0, 1},  {1, 1}};
char dirchar[4] = {'<', '^', '>', 'v'};

// [a,b)
int irand(int a, int b) {
    static mt19937 Rand(static_cast<unsigned int>(time(nullptr)));
    uniform_int_distribution<int> dist(a, b - 1);
    return dist(Rand);
}

// [a,b)
double drand(int a, int b) {
    static mt19937 Rand(static_cast<unsigned int>(time(nullptr)));
    uniform_real_distribution<double> dist(a, b);
    return dist(Rand);
}

// https://qiita.com/IgnorantCoder/items/3101d6276e9bdddf872c
template <typename A, typename F>
inline auto transform(const A &v, F &&f) {
    using result_type =
        decltype(std::declval<F>()(std::declval<typename A::value_type>()));
    vector<result_type> y(v.size());
    std::transform(std::cbegin(v), std::cend(v), std::begin(y), f);
    return y;
}

// 多次元vector生成
template <class T>
vector<T> make_v(size_t size, const T &init) {
    return vector<T>(size, init);
}
template <class... Ts>
auto make_v(size_t size, Ts... rest) {
    return vector<decltype(make_v(rest...))>(size, make_v(rest...));
}

template <typename T>
T Max(vector<T> a) {
    return *max_element(all(a));
}
template <typename T>
T Min(vector<T> a) {
    return *min_element(all(a));
}
template <typename T>
T Sum(vector<T> a) {
    return accumulate(all(a), (T)0);
}

// mapでカウントとかする
template <typename T>
void Add(map<T, int> &m, T item) {
    if (m.find(item) == m.end()) {
        m[item] = 1;
    } else {
        m[item]++;
    }
}

// mapでカウントとかする
template <typename T>
void Erase(map<T, int> &m, T item) {
    if (m.find(item) == m.end()) {
    } else {
        if (m[item] == 1) {
            m.erase(item);
        } else {
            m[item]--;
        }
    }
}

// デフォルト値つきのmapのget
template <typename T, typename U>
U Get(map<T, U> m, T key, U def) {
    if (m.find(key) == m.end()) {
        return def;
    } else {
        return m[key];
    }
}

template <typename T>
inline bool Contains(const set<T> &t, const T &key) {
    return t.find(key) != t.end();
}

template <typename T, typename U>
inline bool Contains(const map<T, U> &t, const T &key) {
    return t.find(key) != t.end();
}

template <class T>
struct Edge {
    int from, to;
    T cost;
    bool operator<(Edge e) {
        return cost < e.cost;
    }
    Edge(int f, int t, T c) : from(f), to(t), cost(c) {}
};

template <class T>
ostream &operator<<(ostream &os, Edge<T> &edge) {
    os << "(" << edge.from << "->" << edge.to << ":" << edge.cost << ")";
    return os;
}
template <class T = int>
class Graph {
    int n;
    bool directed;
    vector<vector<Edge<T>>> edges;

  public:
    Graph(int n, bool directed)
        : n(n), directed(directed), edges(vector<vector<Edge<T>>>(n)) {}

    void add_edge(int s, int t, T cost) {
        edges[s].emplace_back(s, t, cost);
        if (!directed) {
            edges[t].emplace_back(t, s, cost);
        }
    }
    Graph() {}

    vector<Edge<T>> operator[](size_t i) const {
        return edges[i];
    }

    int size() const {
        return n;
    }
};

//======================================================

class SCCD {
  public:
    stack<int> post;
    vb used;

    inline void dfs(int pos, int par, const Graph<int> &g) {
        used[pos] = true;
        for (const auto &e : g[pos]) {
            if (used[e.to]) continue;
            dfs(e.to, pos, g);
        }
        post.push(pos);
    }

    inline void dfsrev(int pos, int par, const Graph<int> &rev, vi &group) {
        used[pos] = true;
        group.push_back(pos);
        for (const auto &e : rev[pos]) {
            if (used[e.to]) continue;
            dfsrev(e.to, pos, rev, group);
        }
    }

    Graph<int> SCC(const Graph<int> &G, vvi &scc, vi &n2g, Graph<int> &dag) {
        int n = G.size();
        Graph<int> rev(n, true);
        // 逆辺グラフの作成
        rep(i, n) {
            rep(j, G[i].size()) {
                auto e = G[i][j];
                rev.add_edge(e.to, e.from, 1);
            }
        }

        // 1 回目の DFS
        used = vb(n, false);
        rep(i, n) {
            if (!used[i]) dfs(i, -1, G);
        }

        // 2 回目の DFS
        fill(all(used), false);
        while (!post.empty()) {
            int pos = post.top();
            post.pop();
            if (used[pos]) continue;
            vi group;
            dfsrev(pos, -1, rev, group);
            scc.push_back(group);
        }

        // 頂点番号から強連結成分の番号を得る辞書の作成
        rep(i, scc.size()) {
            rep(j, scc[i].size()) {
                n2g[scc[i][j]] = i;
            }
        }

        dag = Graph<int>(scc.size(), true);
        set<pair<int, int>> usedEdges;

        // DAG を作成
        rep(i, n) {
            for (const auto &e : G[i]) {
                int s = n2g[e.from];
                int t = n2g[e.to];
                if (usedEdges.find(mp(s, t)) == usedEdges.end() && s != t) {
                    dag.add_edge(s, t, 1);
                    usedEdges.insert(mp(s, t));
                }
            }
        }
        return dag;
    }
};

int longest_path(int pos, const Graph<int> &g, vi &len) {
    if (len[pos] != -1) return len[pos];
    int ans = 0;
    for (auto e : g[pos]) {
        chmax(ans, longest_path(e.to, g, len) + 1);
    }
    return len[pos] = ans;
}

int main() {
    int N;
    scanf("%d", &N);
    vvi idx(N, vi(N));

    int cur = 0;
    rep(i, N) {
        rep(j, i) {
            idx[j][i] = cur;
            cur++;
        }
    }

    Graph<int> G(N * (N - 1) / 2, true);
    rep(i, N) {
        int prev;
        scanf("%d", &prev);
        prev--;
        rep(j, N - 2) {
            int a;
            scanf("%d", &a);
            a--;
            G.add_edge(idx[min(i, prev)][max(i, prev)],
                       idx[min(i, a)][max(i, a)], 1);
            prev = a;
        }
    }

    vvi scc;
    vi n2g(N * (N - 1) / 2);
    SCCD sccd;
    Graph<int> dag;
    sccd.SCC(G, scc, n2g, dag);
    if (dag.size() != N * (N - 1) / 2) {
        cout << -1 << endl;
        return 0;
    }

    vi len(N * (N - 1) / 2, -1);
    rep(i, N * (N - 1) / 2) {
        longest_path(i, dag, len);
    }
    cout << Max(len) + 1 << endl;

    return 0;
}

Measured memory_bytes: 189736