// template version 1.12
using namespace std;
#include <iostream>
#include <bits/stdc++.h>

// varibable settings
#define infile "../test/sample-1.in"
#define int long long //{{{
const int INF=1e18;
const int MOD=1e9+7; //}}}

// define basic macro {{{
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)((b)-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define each(i,a) for (auto&& i : a)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x)-A.begin())
#define posu(A, x) (upper_bound(all(A),x)-A.begin())
template<class T> inline void chmax(T &a, const T &b) { if((a) < (b)) (a) = (b); }
template<class T> inline void chmin(T &a, const T &b) { if((a) > (b)) (a) = (b); }

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;

template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

#if defined(PCM) || defined(LOCAL)
  #include "lib/dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
//}}}

struct pair_hash {
    template <class T1, class T2>
    std::size_t operator () (const std::pair<T1,T2> &p) const {
        auto h1 = std::hash<T1>{}(p.first);
        auto h2 = std::hash<T2>{}(p.second);

        // Mainly for demonstration purposes, i.e. works but is overly simple
        // In the real world, use sth. like boost.hash_combine
        return h1 ^ h2;  
    }
};

int solve(){
  int n;cin>>n;
  int m = n*(n-1)/2;

  vvi M(n);
  rep(i, n){
    rep(j, n-1){
      int a;cin>>a;a--;
      M[i].pb(a);
    }
  }
  dump_2d(M, n, n-1);

  vector<pii> nodes;
  rep(i, n)rep(j, i+1, n){
    nodes.pb(mp(i, j));
  }

  map<pii, vector<pii>> g;
  vvi h(n, vi(n));
  rep(i, n){
    rep(j, 1, n-1){
      int pre = M[i][j-1];
      int to = M[i][j];
      g[mp(min(i, pre), max(i, pre))].pb(mp(min(i, to), max(i, to)));
      h[i][to]++;
      h[to][i]++;
    }
  }
  dump(g);

  //入次数が0の頂点の集合
  stack<pii> st;

  //入次数が0の頂点であればstに追加
  each(i, nodes) if(h[i.first][i.second] == 0) st.push(i);
  
  //ソートされた後のグラフ
  set<pii> finish;

  //stがなくなるまでループ
  int cnt = 0;
  while(sz(finish)<m){
    stack<pii> nex;
    while(st.size()) {
      //stの集合のから一つ取り出す
      pii i = st.top(); st.pop();
      finish.insert(i);

      rep(k, sz(g[i])){
        //隣接する頂点の入次数をマイナス1
        auto j = g[i][k];
        h[j.first][j.second]--;
        h[j.second][j.first]--;
        if (h[j.first][j.second]==0) nex.push(j);
      }
    }

    cnt++;
    dump(cnt, finish);

    //これによって入次数が0になればstに追加
    st = (nex);
    if (sz(st)==0) break;
  }
  
  //ansを順に出力
  dump(finish);
  if (sz(finish)==m) {
    cout << cnt << endl;
  }
  else{
    cout << -1 << endl;
  }
  return 0;
}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
  solve();
  return 0;
} //}}}


Measured memory_bytes: 125940