#include <bits/stdc++.h>
using namespace std;
map<char, int> mp;
int n, m, k;
int main() {
  std::ios::sync_with_stdio(false);
  long long n;
  cin >> n;
  long long ans = 0;
  for (double i = 8.0 / 3; i < 2 * n / sqrt(3); i += 2) {
    double tmp = (sqrt(16.0 * n * n / 3 - 3 * i * i) - i) / 2.0 - 2.0 / 3;
    if (tmp > 0) ans += (long long)tmp / 2 + 1;
  }
  cout << ans * 6 + 1 << endl;
}
