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