#include <bits/stdc++.h>
#include <boost/range/algorithm.hpp>
#include <boost/range/numeric.hpp>
#include <boost/integer/common_factor.hpp>
#include <boost/integer/common_factor_rt.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>

using std::string;
using std::vector;
using std::set;
using std::multiset;
using std::unordered_set;
using std::map;
using std::multimap;
using std::unordered_map;
using std::pair;
using std::cin;
using std::cout;

using boost::multiprecision::cpp_int;
using cpp_dec_float_1000 = boost::multiprecision::number<boost::multiprecision::cpp_dec_float<1000, boost::int128_type>>;

typedef uintmax_t    ull;
typedef intmax_t     ll;
typedef uint64_t     ul;
typedef uint32_t     ui;
typedef uint8_t      uc;

constexpr char CRLF  = '\n';
constexpr char SPACE = ' ';
constexpr char VECTOR_COUT_SEPARATOR = SPACE;
constexpr ll INF = 1000'000'007;
constexpr int MOD = 1000'000'007;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> std::ostream& operator<< (std::ostream& os, const std::vector<T>& vc) { for(auto it = vc.begin(); it != vc.end(); ++it) { if (std::next(it) == vc.end()) os << *it; else os << *it << VECTOR_COUT_SEPARATOR; } return os; }
template<class T1, class T2> inline std::ostream & operator<< (std::ostream & os, const std::pair<T1, T2> & p) { return os << p.first << ' ' << p.second; }
template<class T> T modinv(T a, T m) { T b = m, u = 1, v = 0; while (b) { T t = a / b; a -= t * b; boost::swap(a, b); u -= t * v; boost::swap(u, v); } u %= m; if (u < 0) u += m; return u; }
template<class T> inline bool isSosuu(const T& n) { if (n == T(1)) { return false; } for (T i = 2; i*i <= n; ++i) { if (n % i == 0) { return false; } } return true; }
template<class T> vector<vector<T>> split (const vector<T>& S, T delim) { vector<vector<T>> ret{}; vector<T> buff{}; for (auto c : S) { if (c == delim) { if (!buff.empty()) ret.push_back(buff); buff.clear(); } else { buff.push_back(c); } } if (!buff.empty()) ret.push_back(buff); return ret; }
template<class T> inline void printYesNo(const T& t) { cout << (t ? "Yes" : "No") << CRLF; }
template<class T = int64_t> T modpow(T N, T P, T M) { T ret{1}; N %= M; while (P) { if (P & 0x01) { ret *= N; ret %= M; } P >>= 1; N *= N; N %= M; } return ret; }

/** code for assert debug begin */
int gErr = 0;
#define ASSERT(p) if(!(p)){ gErr = 1; }else{ ; }
/** code for assert debug end */

struct Tmp
{
public:
  using P = pair<int, int>;
  int N;
  vector<P> gameList;
  map<P*, vector<P*>> graph;
  vector<vector<P*>> A;
  map<P*, int> seen;
  map<P*, int> finished;
  vector<P*> hist;
  int rankMax = -1;

  Tmp(int N)
  : N(N)
  , gameList()
  , graph()
  , A(N+1, vector<P*>(N+1, nullptr))
  {
    gameList.reserve(N*N+2);
    for (int i = 0; i < N; ++i) {
      for (int j = i+1; j < N; ++j) {
        gameList.push_back({i, j});
        auto g = &gameList.back();
        A[i][j] = g;
        A[j][i] = g;
      }
    }
  }

  void operator()() {
    input();
    for (int i = 0; i < N; ++i) {
      for (int j = i+1; j < N; ++j) {
        P *g = A[i][j];
        if (!seen[g]) {
          if (rec(g) == -1) {
            cout << -1 << CRLF;
            return;
          }
        }
      }
    }
    cout << rankMax << CRLF;
  }

  int rec(P *game) {
    int *curRank = &seen[game];
    *curRank = 1;
    for (P *nextGame : graph[game]) {
      int *prevRank = &seen[nextGame];
      if (*prevRank) {
        if (!finished[nextGame]) {
          return -1;
        }
        chmax(*curRank, *prevRank + 1);
        continue;
      }
      if (rec(nextGame) == -1) {
        return -1;
      }
      chmax(*curRank, *prevRank + 1);
    }
    chmax(rankMax, *curRank);
    finished[game] = 1;
    return 0;
  }

  void input() {
    for (int i = 0; i < N; ++i) {
      P *lastGame = nullptr;
      for (int j = 0; j < N; ++j) {
        if (i == j)
          continue;
        int a; cin >> a;
        --a;
        auto nextGame = A[i][a];
        if (lastGame) {
          graph[lastGame].push_back(nextGame);
        }
        lastGame = nextGame;
      }
    }
  }
};

void solve(void)
{
  int N; cin >> N;
  Tmp t(N);
  t();
  return;
}

int main(void)
{
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(0);

  solve();

  return 0;
}


Measured memory_bytes: 130432