#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <tuple>
#include <iomanip>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n)-1; i >= 0; i--)
#define pb push_back
#define f first
#define s second
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll max3(ll a, ll b, ll c){return max(a, max(b, c));};
ll min3(ll a, ll b, ll c){return min(a, min(b, c));};
ll max4(ll a, ll b, ll c, ll d){return max(max(a, b), min(c, d));};
ll min4(ll a, ll b, ll c, ll d){return min(min(a, b), min(c, d));};
ll max5(ll a, ll b, ll c, ll d, ll e){return max(max(a, b), max3(c, d, e));};
ll min5(ll a, ll b, ll c, ll d, ll e){return min(min(a, b), min3(c, d, e));};

const ll INFL = 1LL << 60;//10^18 = 2^60
const int INF = 1 << 30;//10^9
ll MOD = 1000000007;
//ll MOD = 998244353;

vector<ll> dy = {0, 0, 1, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, -1, 0, 0, 1, -1, 1, -1, 0};


ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}
ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}

ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll x, ll y){return x / gcd(x, y) * y;};

ll kai_mod(ll x){
  if(x == 0) return 1;
  return x * kai_mod(x-1) % MOD;
}

/*
//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}
*/
ll N;
vector<ll> A[1010];
vector<ll> E[1000010];
vector<ll> d(1000010);
vector<ll> in(1000010);
void solve(){
  ll cnt = 0;
  set<ll> set0, next;
  rep(i, 1000010) if(in[i] == 0) set0.insert(i);

  ll ans = 0;
  while(set0.size()){
    for(auto itr = set0.begin(); itr != set0.end(); itr++){
      for(ll to : E[*itr]){
        in[to]--;
        if(in[to] == 0) next.insert(to);

      }
    }
    set0 = next;
    next.clear();
    cnt++;
  }
  bool l = 0;
  rep(i, 1000010) if(in[i]) cnt = -1;
  cout << cnt << endl;
}

int main(){
  cin >> N;
  rep(i, N){
    rep(j, N-1){
      ll a;
      cin >> a;
      a--;
      A[i].pb(a);
    }
  }


  rep(i, N){
    rep(j, N-2){
      ll a = i;
      ll b = A[i][j];
      ll c = i;
      ll d = A[i][j+1];
      if(a > b) swap(a, b);
      if(c > d) swap(c, d);
      E[a*N + b].pb(c*N + d);
      in[c*N + d]++;
    }
  }
  rep(i, N*N){
    if(E[i].size() <= 1) continue;
    sort(E[i].begin(), E[i].end());
    E[i].erase(unique(E[i].begin(), E[i].end()), E[i].end());
  }
  solve();
}


Measured memory_bytes: 88320