/* -*- coding: utf-8 -*-
 *
 * 3341.cc:  No.3341 Making Beautiful Graphs - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 50;
const int MAX_NN = MAX_N * MAX_N;

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  if (n <= 2) { puts("-1"); return 0; }

  int nn = n * n;

  printf("%d\n", nn * 2);
  for (int i = 0, u = 0; i < n; i++)
    for (int j = 0; j < n; j++, u++) {
      int v0 = (u + n) % nn, v1 = (u + 1) % nn;
      printf("%d %d\n", u + 1, v0 + 1);
      printf("%d %d\n", u + 1, v1 + 1);
    }

  return 0;
}