#include <bits/stdc++.h>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = mod * mod;
const int INF_N = 1e+9;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);
//typedef vector<vector<ll>> mat;
typedef vector<int> vec;

//繰り返し二乗法
ll mod_pow(ll a, ll n, ll m) {
	ll res = 1;
	while (n) {
		if (n & 1)res = res * a%m;
		a = a * a%m; n >>= 1;
	}
	return res;
}

struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n%mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint &a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint &a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint &a, modint b) { a.n = ((ll)a.n*b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, int n) {
	if (n == 0)return modint(1);
	modint res = (a*a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

//逆元(Eucledean algorithm)
ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p%a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }

const int max_n = 1 << 18;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}
using mP = pair<modint, modint>;

int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };


vec memo(1005);
queue<int> v[1005];

void solve() {
    int N; cin >> N;
    auto tmemo = memo;
    rep1(i, N){
        rep(j, N-1){
            int a; cin >> a;
            v[i].push(a);
        }
    }
    int res = 0;
    while(1){
        bool f = false;
        memo = tmemo;
        rep1(i, N){
            if(v[i].empty()) continue;
            int tmp = v[i].front();
            if(memo[i] || memo[tmp]) continue;
            if(v[tmp].front() == i){
                f = true;
                v[i].pop(); v[tmp].pop();
                memo[i] = memo[tmp] = 1;
            }
        }
        if(!f) break;
        res++;
    }
    rep1(i, N){
        if(!v[i].empty()){
            cout << -1 << endl;
            return;
        }
    }
    cout << res << endl;
}

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  //cout << fixed << setprecision(10);
  //init_f();
  //init();
  //int t; cin >> t; rep(i, t)solve();
  solve();
//   stop
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define whole(x) (x).begin(),(x).end()
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
using P = pair<int, int>;
#define debug(var) cerr << "[" << #var << "] " << var << endl
const ll mod = 1000000007;

vector<int> to[500000];
int tab[1005][1005];

int toID(int i, int j) {
    if (i>j) swap(i, j);
    return tab[i][j];
}

int dp[500000];
bool used[500000];
bool calculated[500000];

int dfs(int x) {
    if (used[x]) {
        if (!calculated[x]) return -1;
        return dp[x];
    }
    used[x] = true;
    int now = 1;
    for (int e: to[x]) {
        int res = dfs(e);
        if (res<0) return -1;
        now = max(res+1, now);
    }
    dp[x] = now;
    calculated[x] = true;
    return dp[x];
}

int main(){
    int n;
    cin >> n;
    vector<vector<int>> a(n, vector<int>(n-1));
    rep(i, n) rep(j, n-1) {
        cin >> a[i][j];
        a[i][j]--;
    }
    int id = 0;
    rep(i, n) rep(j, n) {
        if (i<j) tab[i][j] = id++;
    }
    rep(i, n) {
        rep(j, n-1) {
            a[i][j] = toID(i, a[i][j]);
        }
        rep(j, n-2) {
            to[a[i][j]].push_back(a[i][j+1]);
        }
    }

    
    int ans = 0;
    rep(i, id) {
        int res = dfs(i);
        ans = max(ans, res);
        if (res==-1) {
            cout << "-1" << endl;
            return 0;
        }
    }
    
    
    
    cout << ans << endl;
    return 0;
}
