#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  cout << (n + 2) / 2 << '\n';
  for (int i = 0; i < n; ++i)
    cout << i / 2 + 1 << " " << (i + 1) / 2 + 1 << '\n';
  return 0;
}
