#ifdef LOCAL111
	#define _GLIBCXX_DEBUG
#else
	#pragma GCC optimize ("O3")
	#define NDEBUG
#endif
// #define _USE_MATH_DEFINES
#include <bits/stdc++.h>
const int INF = 1e9;
using namespace std;
template<typename T, typename U> ostream& operator<< (ostream& os, const pair<T,U>& p) { os << '(' << p.first << ' ' << p.second << ')'; return os; }

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
	template<typename T> void dpite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
#else
	#define DEBUG(x) true
	template<typename T> void dpite(T a, T b){ return; }
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

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...));
}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value!=0>::type
fill_v(U &u,const V... v){u=U(v...);}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value==0>::type
fill_v(U &u,const V... v){
  for(auto &e:u) fill_v<T>(e,v...);
}

const array<int, 4> dx = {0, 1, 0, -1};
const array<int, 4> dy = {1, 0, -1, 0};


typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);
}


// 検証しなおしたい

//library
typedef long long cost_t;

class Edge {
public:
	int to = -1;
	cost_t cost = -1;
	
	Edge(){
	}

	Edge(int x,cost_t y){
		to = x;
		cost = y;
	}

	// Edge(int x, int y, cost_t z){
	// 	// from = x;
	// 	to = y;
	// 	cost = z;
	// }

	// Edge(int x, int y, int r, cost_t z){
	// 	// from = x;
	// 	to = y;
	// 	cost = z;
	// 	// rev = r;
	// }

	bool operator< (const Edge& x) const {
		if(cost != x.cost) return cost < x.cost;
		return to < x.to;
	}

	bool operator> (const Edge& x) const {
		if(cost != x.cost) return cost > x.cost;
		return to > x.to;
	}
};

class Graph {
private:
	typedef vector<Edge> Edges;
	//const long long int INF = (long long)1e18;
	vector<Edges> v; 
	int n;
public:
	Graph(int x){
		n = x;
		v = vector<Edges>(x);
	}

	Graph(){}

	Edges& operator[](int x){
		return v[x];
	}

	const Edges& operator[](int x) const {
		return v[x];
	}

	int size() const {
		return n;
	}

	void add_edge(int from, const Edge &e){
		v[from].push_back(e);
	}

	void add_edge(int from, int to, cost_t cost = -1){
		add_edge(from,Edge(to,cost));
	}

	// void add_edge(int from, int to, cost_t cost = -1, int rev = -1){
	// 	add_edge(from,Edge(from,to,rev,cost));
	// }

	void add_uedge(int from, int to, cost_t cost = -1){
		add_edge(from,to,cost);
		add_edge(to,from,cost);
	}
};



tuple<vector<int>,int> getSCCDecomposition(const Graph &g)
{
	int n = g.size();
	vector<bool> used(n,false);
	vector<int> cmp(g.size());
	Graph rg(n);
	for(int i = 0; i < n; ++i) {
		for(auto&& e : g[i]) {
			rg.add_edge(e.to,i,e.cost);
		}
	}
	vector<int> vs;
	vs.reserve(g.size());
	
	function<void(int)> dfs = [&](int v){
		used[v] = true;
		for(auto&& e : g[v]) {
			if(!used[e.to]) dfs(e.to);
		}
		vs.push_back(v);
	};

	function<void(int,int)> rdfs = [&](int v, int k){
		used[v] = true;
		cmp[v] = k;
		for(auto&& e : rg[v]) {
			if(!used[e.to]) rdfs(e.to,k); 
		}
	};

	for(int v = 0; v < n; ++v) {
		if(!used[v]) dfs(v);
	}
	fill(used.begin(), used.end(), false);
	int k = 0;
	for(int i = n-1; i >= 0; --i) {
		if(!used[vs[i]]) rdfs(vs[i], k++);
	}
	return make_tuple(cmp,k);
}


int main()
{
	ios_init();
	int n;
	while(cin >> n) {
		auto a = make_v<int>(n, n - 1);
		REP(i, n) {
			REP(j, n - 1) cin >> a[i][j];
		}

		REP(i, n) {
			REP(j, n - 1) a[i][j]--;
		}

		Graph g(n * n);
		bool ex = true;
		REP(i, n) {
			REP(j, n - 2) {
				int fx = i;
				int fy = a[i][j];
				int tx = i;
				int ty = a[i][j + 1];
				if(fx > fy)  swap(fx, fy);
				if(tx > ty) swap(tx, ty);
				int a = fx * n + fy;
				int b = tx * n + ty;
				if(a == b) {
					ex = false;
				}
				g.add_edge(a, b);
			}
		}
		DEBUG(ex);

		int sk;
		tie(ignore, sk) = getSCCDecomposition(g);
		DEBUG(sk);
		if(sk != SZ(g)) {
			ex = false;
		}

		if(!ex) {
			cout << -1 << endl;
		} else {
			vector<int> dp(SZ(g), -1);
			function<int(int)> rec = [&](int v) {
				DEBUG(v);
				if(dp[v] != -1) return dp[v];
				DEBUG(v);
				int res = 0;
				for(auto&& e : g[v]) {
					chmax(res, rec(e.to));
				}
				return dp[v] = res + 1;
			};
			int ans = 0;
			REP(i, n * n) chmax(ans, rec(i));
			cout << ans << endl;
		}

	}
	return 0;
}


Measured memory_bytes: 113792