#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

struct Init{
  Init(){
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
}init;

/**
 * @brief priority queueを使ったtopological sort
 * @return true ならば トポロジカルソートが可能 <=> 閉路がない
 */
bool tsort_priority_queue(const vector<vector<int>> &graph, vector<int> &ret){
  int n = graph.size();
  vector<int> indeg(n);
  REP(i,n){
    for(auto j : graph[i]){
      ++indeg[j];
    }
  }
  priority_queue<int,vector<int>,greater<int>> q;
  REV(i,n-1,0){
    if(indeg[i] == 0) q.push(i);
  }

  while(!q.empty()){
    int cur = q.top(); q.pop();
    ret.push_back(cur);
    for(auto next : graph[cur]){
      --indeg[next];
      if(indeg[next]==0){
        q.push(next);
      }
    }
  }
    
  return (int)ret.size() == n;
}





int main(){
  int N;
  while(cin >> N){
    vector<vector<int>> A(N, vector<int>(N-1)); cin >> A;

    //dump(A);

    

    map<pair<int,int>, int> m;
    {
      int k = 0;
      REP(i,N){
        FOR(j,i+1,N){
          m[{i+1,j+1}] = k;
          m[{j+1,i+1}] = k;
          ++k;
        }
      }
    }
    
    //dump(m);

    int sz = N*(N-1)/2;
    vector<vector<int>> g(sz);
    vector<int> deg(sz);
    
    REP(i,N){
      REP(j,A[i].size()-1){
        int x = i+1;
        int y = A[i][j];
        int z = A[i][j+1];

        int k = m[make_pair(x,y)];
        int l = m[make_pair(x,z)];
        g[k].push_back(l);

        deg[l]++;
      }
    }

    dump(g);

    vector<int> ret;
    if(not tsort_priority_queue(g,ret)){
      cout << -1 << endl;
    }else{
      int ans = 0;

      vector<int> dp(sz);

      queue<int> q;
      REP(i,sz){
        if(deg[i] == 0){
          q.push(i);
          dp[i] = 1;
        }
      }

      while(q.size()){
        int cur = q.front(); q.pop();

        for(auto &nxt : g[cur]){
          deg[nxt]--;

          chmax(dp[nxt], dp[cur]+1);

          if(deg[nxt] == 0){
            q.push(nxt);
          }
        }
      }

      ans = *max_element(ALL(dp));

      cout << ans << endl;
    }
    
  }


  return 0;
}


Measured memory_bytes: 100084