#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  if (n <= 2) {
    cout << -1 << '\n';
  }
  else {
    const int m = n * n;
    vector<pair<int, int>> v;
    rep(i, m) {
      v.push_back({ i, (i - 1 + m) % m });
      v.push_back({ i, (i + 1 + m) % m });
      v.push_back({ i, (i - n + m) % m });
      v.push_back({ i, (i + n + m) % m });
    }
    for (auto&& [x, y] : v)
      if (x > y) swap(x, y);
    set<pair<int, int>> st(v.begin(), v.end());

    cout << st.size() << '\n';
    for (auto [x, y] : st) cout << x + 1 << ' ' << y + 1 << '\n';
  }
  return 0;
}