#include <bitset>
#include <cmath>
#include <fstream>

std::ifstream cin("ciur.in");
std::ofstream cout("ciur.out");

#define NMAX 2000005
std::bitset<NMAX> notPrime;

int main() {
  int n;
  cin >> n;
  for (int p = 2; p <= std::sqrt(n); p++) {
    if (!notPrime[p]) {
      for (int i = p * p; i <= n; i += p) {
        notPrime[i] = 1;
      }
    }
  }
  int count = 0;
  for (int p = 2; p <= n; p++) {
    count += !notPrime[p];
  }
  cout << count;
  return 0;
}