#include <bits/stdc++.h>
#define whlie while
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define rep(i,N) for(int i = 0; i < (N); i++)
#define repr(i,N) for(int i = (N) - 1; i >= 0; i--)
#define rep1(i,N) for(int i = 1; i <= (N) ; i++)
#define repr1(i,N) for(int i = (N) ; i > 0 ; i--)
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define vrep(v,it) for(auto it = v.begin(); it != v.end(); it++)
#define vrepr(v,it) for(auto it = v.rbegin(); it != v.rend(); it++)
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
#define rand rng
using namespace std; void solve();
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vvi = vector< vector<int> >;
constexpr int inf = 1001001001;
constexpr ll infLL = (1LL << 61) - 1;

struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); rep(i,s) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);cout << endl;} while(0)
  int main(){solve_dbg();}
#else
  #define trc(...)
  #define trca(...)
  int main(){solve();}
#endif

using P = pair<int,int>;
constexpr int MOD = 998244853;
mt19937_64 rng(58);
template<typename T>inline T ceil(T a,T b){return (a + b - 1) / b;}
/////////

// トポロジカルソート 任意のグラフに使用可能(たぶん) O(E+V)
// DAGであるときはtrueを、閉路が存在するときfalseを返す
template<typename T>
bool TopologicalSort(vector<int> &v , T &g){
  int N = g.size();
  vector<int> marked(N , 0) , temp(N , 0);
  v.clear(); v.reserve(N);
  // 訪問して帰りがけ順にvに追加
  auto visit = [&](auto f, int i) -> bool{
    if(temp[i] == 1) return false;
    if(marked[i] == 0){
      temp[i] = 1;
      for(auto &e : g[i]){
        if(f(f , e) == false) return false;
      }
      marked[i] = 1;
      v.push_back(i);
      temp[i] = 0;
    }
    return true;
  };

  for(int i = 0 ; i < N ; i++){
    if(marked[i] == 0) {
      if(visit(visit , i) == false) return false;
    }
  }
  reverse( v.begin() , v.end() );
  return true;
}

vvi g;

void solve(){
  ini(N);
  vvi a(N , vi(N - 1));
  rep(i , N) in(a[i]);
  rep(i,N) rep(j,N - 1) a[i][j]--;
  rep(i , N) rep(j , N - 1){
    a[i][j] = min(i , a[i][j]) * N + max(i , a[i][j]);
  }
  rep(i,N) trc(a[i]);
  g.resize(N * N);
  rep(i , N) rep(j , N - 2){
    g[a[i][j]].pb(a[i][j + 1]);
  }
  trc("HOGE");

  vi topo;
  if(TopologicalSort(topo , g) == false) die(-1);
  {  
    vi topo2; topo2.reserve(N * (N - 1) / 2);
    each(x,topo){
      if(x / N < x % N) topo2.pb(x);
    }
    topo.swap(topo2);
  }
  trc(topo);

  vi inv(N*N , -1);
  rep(i , sz(topo)) inv[topo[i]] = i;
  trc(inv);

  vi ans(sz(topo) , 1);
  int cnt = 0;
  each(i , topo){
    if(g[i].empty()) continue;
    each(x , g[i]){
      amax( ans[inv[x]] , ans[inv[i]] + 1 );
      amax( cnt , ans[inv[x]]);
    }
  }
  trc(ans);
  out(cnt);


}


Measured memory_bytes: 55040