/* -*- coding: utf-8 -*-
 *
 * 3192.cc:  No.3192 Diameter Puzzle - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int N = 100;

/* main */

int main() {
  printf("%d\n", N);
  for (int i = 0; i < N; i++) {
    int j = (i + 1) % N;
    printf("%d %d\n", i + 1, j + 1);
  }

  return 0;
}