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

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<vector<int> > mati;
typedef vector<vector<double> > matd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;
typedef vector<pll> vpll;
typedef vector<vpll> vvpll;

#define FOR(i,x,y) for(ll i=(ll)x; i<(ll)y; ++i)
#define REP(i,y) FOR(i, 0, y)
#define RFOR(i,x,y) for(ll i=(ll)x; i>=(ll)y; --i)
#define RREP(i,x) RFOR(i, x, 0)
#define ALL(a) a.begin(), a.end()
#define pb push_back

inline void IN(void){
  return;
}

template <typename First, typename... Rest>
void IN(First& first, Rest&... rest){
  cin >> first;
  IN(rest...);
  return;
}

inline void OUT(void){
  cout << "\n";
  return;
}

template <typename First, typename... Rest>
void OUT(First first, Rest... rest){
  cout << first << " ";
  OUT(rest...);
  return;
}

template <typename T>
void vec_print(vector<T> VEC){
  REP(i, VEC.size()){
    cout << VEC[i] << " ";
  }
  cout << "\n";
};

template <typename T>
void mat_print(vector<vector<T> > MAT){
  REP(i, MAT.size()){
    REP(j, MAT[i].size()){
      cout << MAT[i][j] << " ";
    }
    cout << "\n";
  }
};

template <typename CLASS1, typename CLASS2>
class HOGE{
  public:
    CLASS1 key;
    CLASS2 value;
    HOGE(void){
      return;
    };
    HOGE(CLASS1 key, CLASS2 value){
      this->key = key;
      this->value = value;
    };
    ~HOGE(void){
      return;
    };

    void print(void){
      cout << "key : " << key << ", value : " << value << "\n";
      return;
    };
    
    bool operator==(const HOGE &obj){
      return (this->value == obj.value);
    };
    bool operator<(const HOGE &obj){
      return (this->value < obj.value);
    };
    bool operator>(const HOGE &obj){
      return (this->value > obj.value);
    };
};

template <typename CLASS1, typename CLASS2>
bool operator==(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value == hoge2.value;
};

template <typename CLASS1, typename CLASS2>
bool operator<(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value < hoge2.value;
};

template <typename CLASS1, typename CLASS2>
bool operator>(const HOGE<CLASS1, CLASS2> &hoge1, const HOGE<CLASS1, CLASS2> &hoge2){
  return hoge1.value > hoge2.value;
};

constexpr int INF = (1<<30);
constexpr ll INFLL = 1LL<<62;
constexpr long double EPS = 1e-12;
constexpr ll MOD = (ll)((1E+9)+7);

ll N;
vvll Graph;
vb touch_flag1;
vb touch_flag2;
vll longest_value;

bool find_loop(ll pos, ll value){
  if(touch_flag2[pos]) return false;
  if(touch_flag1[pos]) return true;
  touch_flag1[pos] = true;
  REP(i,Graph[pos].size()){
    if(find_loop(Graph[pos][i], value)){
      return true;
    }
  }
  touch_flag1[pos] = false;
  touch_flag2[pos] = true;
  return false;
}

bool find_loop(ll pos){
  if(touch_flag2[pos]) return false;
  return find_loop(pos, pos);
}

ll search(ll pos){
  ll tmp = 0;
  if(longest_value[pos]>=0) return longest_value[pos];
  REP(i,Graph[pos].size()) tmp = max(tmp, search(Graph[pos][i])+1);
  longest_value[pos] = tmp;
  return tmp;
}

int main(){
  cin.tie(0); // cut the cin and cout (default, std::flush is performed after std::cin)
  ios::sync_with_stdio(false); // cut the iostream and stdio (DON'T endl; BUT "\n";)

  fprintf(stderr, "hoge\n");
  IN(N);
  vvll A(N, vll(N-1));
  REP(i,N){
    REP(j,N-1){
      IN(A[i][j]);
      A[i][j]--;
    }
  }

  fprintf(stderr, "hoge\n");

  Graph.resize(N*N);
  longest_value.resize(N*N, -1);

  REP(i,N){
    REP(j,N-2){
      fprintf(stderr, "%lld %lld\n", i, j);
      ll before_A = A[i][j];
      ll after_A = A[i][j+1];
      ll before_i = i;
      ll after_i = i;
      if(before_i>before_A) swap(before_i, before_A);
      if(after_i>after_A) swap(after_i, after_A);
      ll before = before_i*N+before_A;
      ll after = after_i*N+after_A;
      Graph[before].pb(after);
    }
  }

  fprintf(stderr, "hoge\n");

  touch_flag1.resize(N*N, false);
  touch_flag2.resize(N*N, false);
  REP(i,N){
    FOR(j,i+1,N){
      if(find_loop(i*N+j)){
        OUT(-1);
        return 0;
      }
    }
  }

  fprintf(stderr, "hoge\n");

  ll ans = 0;
  REP(i,N*N){
    ans = max(search(i), ans);
  }

  OUT(ans+1);

  return 0;
}

Measured memory_bytes: 55296