#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int T = 1;
  while (T--) {
    int n;
    cin >> n;
    vector<pair<int, int> > ans;
    ans.push_back(make_pair(1, 1));
    ans.push_back(make_pair(1, 2));
    ans.push_back(make_pair(2, 1));
    ans.push_back(make_pair(2, 2));
    int row = 2, col = 2;
    while (n--) {
      ans.push_back(make_pair(row + 1, col));
      ans.push_back(make_pair(row, col + 1));
      ans.push_back(make_pair(row + 1, col + 1));
      row++;
      col++;
    }
    cout << ans.size() << "\n";
    for (int i = 0; i < ans.size(); i++) {
      cout << ans[i].first << " " << ans[i].second << "\n";
    }
  }
  return 0;
}
