#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
template <typename T>
void show2d(const vector<vector<T>>& adj) {
  for (auto x : adj) {
    for (auto y : x) {
      cout << y << " ";
    }
    cout << "\n";
  }
}
long long int modexp(long long int a, long long int b, long long int mod) {
  long long int x = 1;
  while (b) {
    if (b & 1) x = ((x % mod) * (a % mod)) % mod;
    a = ((a % mod) * (a % mod)) % mod;
    b = b / 2;
  }
  return x;
}
void rf() {}
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  int ch = n - 1;
  int tot = ch * 3 + 7;
  cout << tot << "\n";
  cout << 0 << " " << 0 << "\n";
  cout << 1 << " " << 0 << "\n";
  cout << 0 << " " << 1 << "\n";
  cout << 1 << " " << 1 << "\n";
  cout << 1 << " " << 2 << "\n";
  cout << 2 << " " << 2 << "\n";
  cout << 2 << " " << 1 << "\n";
  for (int i = 2; i <= n; ++i) {
    cout << i << " " << i + 1 << "\n";
    cout << i + 1 << " " << i + 1 << "\n";
    cout << i + 1 << " " << i << "\n";
  }
}
