#ifdef DEBUG_IS_VALID
#define DEB 1 
#define _LIBCPP_DEBUG 0
#else
#define DEB 0
#define NDEBUG
#endif

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

#define ALL(g) (g).begin(),(g).end()
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define RREP(i, x, n) for(int i = x; i >= n; i--)
#define rrep(i, n) RREP(i,n,0)
#define pb push_back
#define fi first
#define se second
#pragma GCC optimize ("-O3")

using namespace std;

#define DUMPOUT cout
#define dump(...) if(DEB) DUMPOUT<<"  "<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl<<"    "; if(DEB) dump_func(__VA_ARGS__)
template<typename T1,typename T2>ostream& operator << (ostream& os, pair<T1,T2> p){cout << "(" << p.first << ", " << p.second << ")"; return os;}
template<typename T>ostream& operator << (ostream& os, vector<T>& vec) { os << "{"; for (int i = 0; i<vec.size(); i++) os << vec[i] << (i + 1 == vec.size() ? "" : ", "); os << "}"; return os; }
template<typename T>ostream& operator << (ostream& os, set<T>& st){cout << "{"; for(auto itr = st.begin(); itr != st.end(); itr++) cout << *itr << (next(itr)!=st.end() ? ", " : ""); cout << "}"; return os;}
template<typename T1,typename T2>ostream& operator << (ostream& os, map<T1,T2> mp){cout << "{"; for(auto itr = mp.begin(); itr != mp.end(); itr++) cout << "(" << (itr->first) << ", " << (itr->second) << ")" << (next(itr)!=mp.end() ? "," : ""); cout << "}"; return os; }

void dump_func(){DUMPOUT << endl;}
template <class Head, class... Tail>void dump_func(Head&& head, Tail&&... tail){ DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...);}
template<class T> inline bool chmax(T& a,T const& b){if(a>=b) return false; a=b; return true;}
template<class T> inline bool chmin(T& a,T const& b){if(a<=b) return false; a=b; return true;}

using ll = long long;
using P = pair<int,int>;
using Pl = pair<ll,ll>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vp = vector<Pl>;
using vvp = vector<vp>;

const int INF = 1<<29;
const long long LINF=1LL<<59;

vector<int> topological_sort(const vector<vector<int>>& graph){
  // if graph is not DAG, return {}
  // else topological sorted vertices
  int N = graph.size();
  stack<int> st;
  vector<int> h(N), res;
  for(int i = 0; i < N; i++)
    for(auto& v: graph[i]) h[v]++;
  for(int i = 0; i < N; i++)
    if(h[i] == 0) st.push(i);
  while(st.size()) {
    int u = st.top(); st.pop();
    res.push_back(u);
    for(auto& v: graph[u]){
      h[v]--;
      if(h[v] == 0) st.push(v);
    }
  }
  if(res.size() != N) res.clear();
  return res;
}

void solve(long long N, std::vector<std::vector<long long>> A){
  vvi table(N,vi(N,-1));
  int cur = 0;
  rep(i,N) rep(j,N) if(i<j) table[i][j] = (cur++);
  auto enc = [&](int a,int b){
    if(a>b) swap(a,b);
    dump(table[a][b]);
    return table[a][b];
  };
  ll sz = N*(N-1)/2;
  vvi g(sz);
  dump(table,sz);
  dump(A);
  rep(i,N){
    REP(j,1,N-1){
      g[enc(i,A[i][j-1]-1)].pb(enc(i,A[i][j]-1));
    }
  }
  dump(g);
  auto ts = topological_sort(g);
  dump(ts);
  if(ts.size()==0){
    cout << "-1" << endl;
    return;
  }
  vl dp(sz, 0);
  for(auto u:ts){
    for(auto v:g[u]) chmax(dp[v],dp[u]+1LL);
  }
cout << *max_element(ALL(dp))+1LL << endl;
}

int main(){
  std::cout << std::fixed << std::setprecision(15);
  long long N;
  scanf("%lld",&N);
  std::vector<std::vector<long long>> A(N, std::vector<long long>(N-1));
  for(int i = 0 ; i < N ; i++){
    for(int j = 0 ; j < N-1 ; j++){
      scanf("%lld",&A[i][j]);
    }
  }
  solve(N, std::move(A));
  return 0;
}


Measured memory_bytes: 45268