#include <iostream>
#include <array>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <algorithm>
#include <math.h>
#include <string>
#include <climits>
#include <assert.h>
#include <iomanip>
#include <bitset>
#include <queue>
#include <deque>
#include <stack>
#include <functional>
#include <fstream>

#define SIZE(x) int(x.size())
#define FOR(i,a,n) for(int i=(a);i<(n); ++i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define IS_BIT_ON(bit, i) (bit & (1 << i))
#define BIT_ON(bit, i) (bit |= (1 << i))
#define BIT_OFF(bit, i) (bit &= ~(1 << i))
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
void print() { std::cout << std::endl; }
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) { std::cout << head; if (sizeof...(tail) != 0) {std::cout << " ";} print(std::forward<Tail>(tail)...); }
template <class T> void print(std::vector<T> &v) {for (auto& a : v) { std::cout << a; if (&a != &v.back()) {std::cout << " ";} }std::cout << std::endl;}
template <class T> void print(std::vector<std::vector<T>> &vv) { for (auto& v : vv) { print(v); }}
void debug() { std::cerr << std::endl; }
template <class Head, class... Tail> void debug(Head&& head, Tail&&... tail) { std::cerr << head; if (sizeof...(tail) != 0) {std::cerr << " ";} print(std::forward<Tail>(tail)...); }
template <class T> void debug(std::vector<T> &v) {for (auto& a : v) { std::cerr << a; if (&a != &v.back()) {std::cerr << " ";} }std::cerr << std::endl;}
template <class T> void debug(std::vector<std::vector<T>> &vv) { for (auto& v : vv) { print(v); }}
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}

long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 58u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

class TopologicalSort {
    const int N;                           // ノード数
    std::vector<std::vector<int>> graph;   // グラフ
    std::vector<bool> used;                // 使用済みノード
    std::vector<int> indeg;                // 入次数


public:
    std::vector<int> result; // ソート結果

public:
    TopologicalSort(unsigned int num_node) : N(num_node) {
        this->graph.resize(num_node);
        this->indeg.resize(num_node, 0);
        this->used.resize(num_node, false);
    }

    // u -> vのedgeを追加
    void add(int u, int v) {
        assert(u != v);
        this->graph[u].emplace_back(v);
    }

    // O(V + E)
    bool sort() {
        for (int u = 0; u < this->N; ++u) {
            for (int v : this->graph[u]) {
                this->indeg[v]++;
            }
        }

        for (int u = 0; u < this->N; ++u) {
            if (this->indeg[u] == 0 and not this->used[u]) {
                bfs(u);
            }
        }

        return (int)this->result.size() == this->N;
    }

    // グラフの有向パスのうち最長のものの長さ
    // ソート結果が一意ならN - 1になる
    int longest_distance() {
        int ans = 0;
        std::vector<int> distance(this->N, 0);
        for (int u : this->result) {
            for (int v : this->graph[u]) {
                distance[v] = max(distance[v], distance[u] + 1);
                ans = max(ans, distance[v]);
            }
        }

        return ans;
    }

private:
    void bfs(const int s) {
        std::queue<int> que;
        que.push(s);
        this->used[s] = true;
        while (not que.empty()) {
            int u = que.front();
            que.pop();
            this->result.emplace_back(u);

            for (int v : this->graph[u]) {
                this->indeg[v]--;
                if (this->indeg[v] == 0 and not this->used[v]) {
                    this->used[v] = true;
                    que.push(v);
                }
            }
        }
    }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    LL N;
    cin >> N;
    auto A = make_v<int>(N, N - 1);
    map<pair<int, int>, int> number;
    FOR(i, 0, N) {
        FOR(j, 0, N - 1) {
            cin >> A[i][j];
            A[i][j]--;

            int a = min(i, A[i][j]);
            int b = max(i, A[i][j]);
            if (number.count(make_pair(a, b)) == 0) {
                number[make_pair(a, b)] = number.size() - 1;
            }
        }
    }

    TopologicalSort ts(N * (N - 1) / 2);
    FOR(i, 0, N) {
        int pre = -1;
        FOR(j, 0, N - 1) {
            int a = min(i, A[i][j]);
            int b = max(i, A[i][j]);

            int node = number[make_pair(a, b)];
            if (pre != -1) {
                ts.add(pre, node);
            }
            pre = node;
        }
    }
    if (not ts.sort()) {
        print(-1);
        return 0;
    }

    print(ts.longest_distance() + 1);
    
    return 0;
}


Measured memory_bytes: 68848