#include <fstream>

using namespace std;

bool prim[2000005];
int sol, n;

int main () {
  ifstream fi("ciur.in");
  ofstream fo("ciur.out");
  fi >> n;
  for (int i = 2; i <= n; i++)
    prim[i] = true;
  for (int i = 2; i <= n; i++)
    if (prim[i]) {
      sol++;
      for (int j = i+i; j <= n; j += i)
        prim[j] = false;
    }
  fo << sol;
  return 0;
}