#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;

//#define int long long
using bll = boost::multiprecision::cpp_int;
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr int dx[4]={1,0,-1,0};
constexpr int dy[4]={0,1,0,-1};
#ifdef LOCAL_ENV
	#define debug(var) std::cout<<#var" = "<<var<<std::endl
#else
	#define debug(var)
#endif
#define p(var) std::cout<<var<<std::endl
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define all(a) (a).begin(), (a).end()
#define PI (acos(-1))
template<typename T> inline T power(T x, T n){ return n ? power(x*x%MOD,n/2)*(n%2?x:1)%MOD : 1; }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T1, typename T2>inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2>inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
template<typename T1, typename T2> ostream& operator<<(ostream& s, const pair<T1, T2>& p) {return s << "(" << p.first << ", " << p.second << ")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& v) {
	for (int i = 0, len = v.size(); i < len; ++i){
		s << v[i]; if (i < len - 1) s << "\t";
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s, const vector< vector<T> >& vv) {
	for (int i = 0, len = vv.size(); i < len; ++i){
		s << vv[i] << endl;
	}
	return s;
}
template<typename T1, typename T2> ostream& operator<<(ostream& s, const map<T1, T2>& m) {
	s << "{" << endl;
	for (typeof(m.begin()) itr = m.begin(); itr != m.end(); ++itr){
		s << "\t" << (*itr).first << " : " << (*itr).second << endl;
	}
	s << "}" << endl;
	return s;
}

/*-----8<-----8<-----*/

vector<ll> topological_sort(vector<vector<ll>> &g){
	ll gsize=g.size();
	//各頂点の入次数を記録
	vector<ll> indegree(gsize, 0);
	for(ll from=0; from<gsize; from++){
		for(ll to : g[from]){
			indegree[to]++;
		}
	}

	//入次数が0の頂点であればqueueに追加
	queue<ll> que;
	for(ll i=0; i<gsize; i++){
		if(indegree[i]==0)que.push(i);
	}

	//入次数が０の頂点から順にansへ格納
	vector<ll> ans;
	while(!que.empty()){
		ll v=que.front();
		que.pop();
		ans.push_back(v);
		for(ll nextv : g[v]){
			indegree[nextv]--;
			if(indegree[nextv]==0)que.push(nextv);
		}
	}

	//ansへ格納されていない頂点がある＝閉路が存在する
	return ans.size()==gsize ? ans : vector<ll>();
}

vector<ll> longest_path(vector<vector<ll>> &g, vector<ll> &topological){
	ll gsize=g.size();
	vector<ll> dp(gsize, 0);
	vector<ll> nextv(gsize, -1);
	ll maxval = -1;
	ll startv = -1;
	for(auto it = topological.rbegin(); it != topological.rend(); ++it){
		for(ll u : g[*it]){
			if(chmax(dp[*it], dp[u] + 1)) nextv[*it] = u;
		}
		if(chmax(maxval, dp[*it])) startv = *it;
	}

	ll v=startv;
	vector<ll> longest_path;
	while(1){
		longest_path.push_back(v);
		if(nextv[v]==-1)break;
		v=nextv[v];
	}
	return longest_path;
}

signed main() {
	ll N;
	scanf("%lld", &N);
	vector<vector<ll>> a(N, vector<ll>(N-1, 0));

	rep(i, N) rep(j, N-1) {
		ll t;
		scanf("%lld", &t);
		a[i][j]=t-1;
	}

	map<pair<ll,ll>,ll> m;
	ll t=0;
	rep(i,N-1)for(ll j=i+1;j<N;j++){
		if(i==j)continue;
		m[make_pair(i,j)]=t;
		t++;
	}

	vector<vector<ll>> g(m.size());
	rep(i,N){
		pair<ll,ll> pt=a[i][0]<i ? make_pair(a[i][0],i) : make_pair(i,a[i][0]);
		ll from=m[pt];
		repeq(j,N-2){
			pair<ll,ll> ps=a[i][j]<i ? make_pair(a[i][j],i) : make_pair(i,a[i][j]);	
			ll to=m[ps];
			g[from].push_back(to);
			from=to;
		}
	}

	vector<ll> topological=topological_sort(g);
	debug(topological);
	if(topological.size()==0){
		printf("-1\n");
		return 0;
	}

	vector<ll> longest=longest_path(g,topological);
	printf("%zu\n", longest.size());
	return 0;
}


Measured memory_bytes: 86380