#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i;
  cin >> n;
  cout << (n / 2) + 1 << endl;
  for (i = 1; i <= (n / 2) + 1; i++) cout << i << " 1" << endl;
  ;
  if (n % 2 != 0)
    for (i = 2; i <= (n / 2) + 1; i++) cout << (n / 2) + 1 << " " << i << endl;
  else
    for (i = 2; i < (n / 2) + 1; i++) cout << (n / 2) + 1 << " " << i << endl;
}
