//#define NDEBUG
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  constexpr usize operator"" _z(unsigned long long x) noexcept {
    return static_cast<usize>(x);
  }

  class rep {
    const usize f, l;

  public:
    class itr {
      friend rep;
      usize i;
      constexpr itr(const usize x) noexcept : i(x) {}

    public:
      void operator++() noexcept { ++i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
    constexpr itr begin() const noexcept { return itr(f); }
    constexpr itr end() const noexcept { return itr(l); }
  };
  class revrep {
    const usize f, l;

  public:
    class itr {
      friend revrep;
      usize i;
      constexpr itr(usize x) noexcept : i(x) {}

    public:
      void operator++() noexcept { --i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
    constexpr itr begin() const noexcept { return itr(l); }
    constexpr itr end() const noexcept { return itr(f); }
  };
  template <class T> using vec_alias = std::vector<T>;
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) {
    return a < b ? b - a : a - b;
  }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }

} // namespace n91

#include <algorithm>
#include <iostream>
#include <set>
#include <utility>

namespace n91 {

  void main_() {
    const usize n = scan<usize>();
    auto a = md_vec(n, n - 1_z, usize());
    for (auto& v : a) {
      for (auto& e : v) {
        e = scan<usize>() - 1_z;
      }
    }
    struct match {
      usize x, y;
    };
    auto pushed = md_vec(n, n, false);
    std::vector<match> cur, nxt;
    for (const auto i : rep(0_z, n)) {
      const usize t = a[i][0_z];
      if (a[t][0_z] == i && !pushed[i][t]) {
        cur.push_back({ i, t });
        pushed[i][t] = true;
        pushed[t][i] = true;
      }
    }
    std::vector<usize> idx(n, 0_z);
    const auto top = [&](const usize i) { return a[i][idx[i]]; };
    usize ans = 0_z;
    while (!cur.empty()) {
      for (const auto& e : cur) {
        ++idx[e.x];
        if (idx[e.x] != n - 1_z) {
          const usize t = top(e.x);
          if (top(t) == e.x && !pushed[e.x][t]) {
            nxt.push_back({ e.x, t });
            pushed[e.x][t] = true;
            pushed[t][e.x] = true;
          }
        }

        ++idx[e.y];
        if (idx[e.y] != n - 1_z) {
          const usize t = top(e.y);
          if (top(t) == e.y && !pushed[e.y][t]) {
            nxt.push_back({ e.y, t });
            pushed[e.y][t] = true;
            pushed[t][e.y] = true;
          }
        }
      }

      cur.clear();
      std::swap(cur, nxt);
      ++ans;
    }
    if (std::all_of(idx.cbegin(), idx.cend(),
      [n](const usize x) { return x == n - 1_z; })) {
      std::cout << ans << std::endl;
    }
    else {
      std::cout << "-1" << std::endl;
    }
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 8320