#include <bits/stdc++.h>
using namespace std;
long long a[1001][1001], ans[1001];
int main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  int x = (n + 1) / 2 + 1 * ((n + 1) & 1);
  vector<pair<int, int> > v;
  for (int j = 1; j <= x; j++) {
    if (v.size() == n) break;
    v.push_back(make_pair(1, j));
  }
  for (int i = 2; i <= x; i++) {
    if (v.size() == n) break;
    v.push_back(make_pair(i, x));
  }
  cout << x << "\n";
  for (pair<int, int> x : v) {
    cout << x.first << " " << x.second << "\n";
  }
  return 0;
}
