/**
 *      purpose : 
 *      author  : kyomukyomupurin
 *      created : 
**/

// input/output
#include <fstream>
#include <iostream>
#include <sstream>
// container class
#include <array>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// math, algorithm
#include <algorithm>
#include <cmath>
#include <complex>
#include <numeric>
// etc
#include <bitset>
#include <cassert>
#include <cctype>
#include <cstring>
#include <chrono>
#include <functional>
#include <iomanip>
#include <random>
#include <utility>
// using-directive
using namespace std;
// alias template
using int64 = long long;
using uint64 = unsigned long long;
using vi = std::vector<int>;
using vl = std::vector<int64>;
using pii = std::pair<int, int>;
using pii = std::pair<int, int>;
using pll = std::pair<int64, int64>;
// text macro replacement
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define all(_) (_).begin(), (_).end()
#define rall(_) (_).rbegin(), (_).rend()
#define print(_) std::cout << (_) << '\n'
#define debug(_) std::cerr << #_ << ": " << (_) << '\n'
#define dbg(vec) for (size_t _ = 0; _ < vec.size(); ++_){std::cerr << #vec << "[" << _ << "] : " << vec[_] << '\n';}
// variadic template
template<typename T> inline void chmin(T &a, T b) {if (a > b) a = b; return;}
template<typename T> inline void chmax(T &a, T b) {if (a < b) a = b; return;}
// constant
const int INF = (1<<30) - 1;  // 1.073741823e9
const int64 INF64 = (1LL<<62) - 1;  // 4.611686018427387903e18
const int MOD = 1000000007;

constexpr int cm = 1<<17;
char buff[cm], *ci = buff + cm, ct;

inline char readchar() {
  if (ci - buff == cm) {
    fread(buff, 1, cm, stdin);
    ci = buff;
  }
  return *ci++;
}

inline int readint() {
  int num = 0;
  if (ci - buff + 16 > cm) {
    while ((ct = readchar()) >= '0') {
      num = (num << 3) + (num << 1) + ct - '0';
    }
  } else {
    while ((ct = *ci++) >= '0') {
      num = (num << 3) + (num << 1) + ct - '0';
    }
  }
  return num;
}

int main(){
  //std::ios_base::sync_with_stdio(false);
  //std::cin.tie(nullptr);
  auto start = std::chrono::system_clock::now();

  int n = readint();

  vector<queue<int>> v(1010, queue<int> ());
  rep(i, n) {
    rep(j, n - 1) {
      int a = readint();
      v[i + 1].push(a);
    }
  }

  for (int day = 1; day <= n * (n - 1) / 2; ++day) {
    bool done[1010] = {};
    for (int i = 1; i <= n; ++i) {
      if (done[i]) continue;
      if (v[i].empty()) continue;
      int next = v[i].front();
      if (done[next]) continue;
      if (v[next].front() == i) {
        v[i].pop(); v[next].pop();
        done[i] = done[next] = true;
      }
    }
    if (all_of(done, done + n, [](const bool& x){return x == false;})){
      cout << -1 << '\n'; return 0;
    }
    if (all_of(v.begin(), v.end(), [](const queue<int>& x){return x.empty();})) {
      cout << day << '\n'; return 0;
    }
    auto now = std::chrono::system_clock::now();
    auto dur = now - start;
    auto msec = std::chrono::duration_cast<std::chrono::milliseconds>(dur).count();
    if (msec >= 1800) {
      cout << n * (n - 1) / 2 << '\n'; return 0;
    }
  }

  return 0;
}

Measured memory_bytes: 4864