#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int n;
  cin >> n;
  if (n <= 2)
  {
    cout << "-1" << endl;
    return 0;
  }
  cout << n * n * 2 << endl;
  for (int i = 0; i < n * n; ++i)
  {
    int v1 = (i + 1) % (n * n) + 1, v2 = (i + n) % (n * n) + 1;
    cout << i + 1 << ' ' << v1 << endl;
    cout << i + 1 << ' ' << v2 << endl;
  }
}