#include <bits/stdc++.h>
using namespace std;
#define INF 1<<30
#define endl '\n'
#define maxn 100005
#define tc printf("Case %d: ", cs)
#define tcn printf("Case %d:\n", cs);
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);

#define dbg1(x) cerr << #x << " = " << x << endl;
#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
#define dbg3(x, y, z) cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
#define dbg4(w,x, y, z) cerr << #w << " = " << w << ", " <<#x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;

template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
	return os << "(" << p.first << ", " << p.second << ")";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
	os << "{";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << *it;
	}
	return os << "}";
}

template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin()) os << ", ";
		os << *it;
	}
	return os << "]";
}

template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
		if ( it != v.begin() ) os << ", ";
		os << it -> first << " = " << it -> second ;
	}
	return os << "]";
}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();
#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>
void faltu( T a[], int n ) {
	for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
	cerr << endl;
}

template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less 
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

/**___________________________________________________**/
const int N = 1e3 + 11, M = 2e6 + 6;
int n;
int a[N][N], indeg[M], dp[M];
vector<int> graph[M];
vector<int> ts;

int ind(int x, int y)
{
	return min(x, y) * N + max(x, y);
}

bool topsort()
{
	//dbg("here");
	queue<int> Q;
	int lmt = ind(n, n);
	//dbg(lmt);
	for (int i = 0; i < lmt; i++) {
		if (indeg[i] == 0) Q.push(i);
	}

	while (!Q.empty()) {
		int u = Q.front();
		Q.pop();
		ts.push_back(u);
		for (auto v : graph[u]) {
			indeg[v]--;
			dp[v] = max(dp[v],  dp[u] + 1);
			if (indeg[v] == 0) Q.push(v);
		}
	}
	return (int)ts.size() == lmt;
}
int main()
{
	FASTIO
	/*
#ifndef ONLINE_JUDGE
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
	freopen("error.txt", "w", stderr);
#endif
//*/
	cin >> n;
	for (int i = 1; i <= n; i++) {
		int last = 0;
		for (int j = 2; j <= n; j++) {
			cin >> a[i][j];
			int x = ind(i, a[i][j]);
			graph[last].push_back(x);
			indeg[x]++;
			last = x;
		}
	}

	if (!topsort()) cout << -1 << endl;
	else cout << *max_element(dp, dp + M) << endl;
}

Measured memory_bytes: 86388