#include <fstream>

using namespace std;

int x, p, i, j;
char marcat[2000005];

int main () {
  ifstream fi("ciur.in");
  ofstream fo("ciur.out");
  fi >> x;
  for (i = 2; i <= x; i++)
    marcat[i] = 1;
  for (i = 2; i <= x; i++)
    if (marcat[i]) {
      p++;
      for (j = i*2; j <= x; j += i)
        marcat[j] = 0;
    }
  fo << p;
  return 0;
}