#include <bits/stdc++.h>
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
#define IOS cin.tie(0),ios::sync_with_stdio(false)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
	if (v.empty())return out;
	constexpr bool is_vector_v = is_vector<T>::value;
	if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
	else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
	return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }

int ans = 0;

vector<int> topologicalSort(vector<vector<int>>& path) {
	int n = (int)path.size();
	vector<int> res;
	vector<int> entry(n, 0);
	queue<int> q;
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < path[i].size(); ++j) {
			entry[path[i][j]]++;
		}
	}
	for (int i = 0; i < n; ++i) {
		if (!entry[i]) {
			q.push(i);
		}
	}
	while (!q.empty()) {
		int p = q.front();
		q.pop();
		res.push_back(p);
		bool flag = false;
		for (int i = 0; i < path[p].size(); ++i) {
			if (--entry[path[p][i]] == 0) {
				q.push(path[p][i]);
				flag = true;
			}
		}
		if (flag) {
			ans++;
		}
	}
	return res;
}

int proc(int i, int j, int n) {
	if (i > j) {
		return i * n + j;
	} else {
		return j * n + i;
	}
}

int main() {
	IOS;
	int n;
	cin >> n;
	vector<vector<int>> a(n, vector<int>(n));
	vector<vector<int>> path(n * n);
	int pre = -1;
	REP(i, n) {
		REP(j, n - 1) {
			int temp;
			cin >> temp;
			temp--;
			if (pre >= 0) {
				int t1 = proc(pre, i, n);
				int t2 = proc(temp, i, n);
				path[t1].push_back(t2);
				
			}
			pre = temp;
		}
		pre = -1;
	}
	vector<int> s = topologicalSort(path);
	if (s.size() != path.size()) {
		put(-1);
		return 0;
	}
	vector<int> dp(n* n, 0);
	int res = 0;
	REP(i, s.size()) {
		int y, x;
		y = s[i] / n;
		x = s[i] % n;
		REP(j, path[s[i]].size()) {
			chmax(dp[path[s[i]][j]], dp[s[i]]+1);
		}
	}
	REP(i, n* n) {
		chmax(res, dp[i]);
	}
	put(res+1);
	return 0;
}

Measured memory_bytes: 54896