#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  cin >> N;
  vector<bool> B(N + 1, true);
  B.at(0) = B.at(1) = false;
  for (int i = 2; i <= N; i++) {
    if (!B.at(i)) continue;
    for (int j = i + i; j <= N; j += i) B.at(j) = false;
  }
  long ans = 0;
  for (int i = 2; i <= N; i++) {
    if (!B.at(i)) continue;
    if (i == 2) {
      ans++;
      continue;
    }
    long tmp = i + 2;
    if (sqrt(tmp) == (long) sqrt(tmp)) {
      long tmp2 = sqrt(tmp);
      if (tmp2 <= N && B.at(tmp2)) ans += 2;
    }
  }
  cout << ans << "\n";
}