#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;


struct TopologicalSort{
  bool is_dag;
  vector<int> sorted;
  
  TopologicalSort(const vector<vector<int>> &g){
    int n = g.size();
    vector<int> indeg(n);
    
    REP(i,n){
      for(auto j : g[i]){
        ++indeg[j];
      }
    }

    queue<int> q;
    REV(i,n-1,0){
      if(indeg[i] == 0) q.push(i);
    }

    while(!q.empty()){
      int cur = q.front(); q.pop();
      sorted.push_back(cur);
      for(auto nxt : g[cur]){
        --indeg[nxt];
        if(indeg[nxt]==0){
          q.push(nxt);
        }
      }
    }
  
    is_dag = (int)sorted.size() == n;
  }
};

int dag_longest_path(const vector<vector<int>> &g){
  int n = g.size();
  vector<int> ret(n);
  vector<bool> visited(n);

  auto dfs =
    [&](auto &f, int cur) -> int{
      if(visited[cur]) return ret[cur];
      visited[cur] = true;

      for(auto &nxt : g[cur]){
        chmax(ret[cur], f(f,nxt) + 1);
      }

      return ret[cur];
    };

  REP(i,n) if(not visited[i]) dfs(dfs,i);

  return *max_element(ALL(ret));
}
  



int main(){
  int N;
  while(cin >> N){
    vector<vector<int>> A(N, vector<int>(N-1)); cin >> A;
    REP(i,N) for(auto &x : A[i]) --x;
    
    vector<vector<int>> m(N, vector<int>(N));
    {
      int k = 0;
      REP(i,N){
        FOR(j,i+1,N){
          m[i][j] = m[j][i] = k;
          ++k;
        }
      }
    }

    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;
        int y = A[i][j];
        int z = A[i][j+1];

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

        deg[l]++;
      }
    }

    auto ts = TopologicalSort(g);

    
    if(not ts.is_dag){
      cout << -1 << endl;
    }else{
      int ans = dag_longest_path(g) + 1;
      cout << ans << endl;
    }
  }

  return 0;
}


Measured memory_bytes: 41588