#include <cstdio>
#include <bitset>
using namespace std;
const int NMAX = 2000505;
bitset<NMAX> mark;
int n;

int main() {
  freopen("ciur.in", "r", stdin);
  freopen("ciur.out", "w", stdout);
  
  scanf("%d", &n);
  for (int i = 2; i * i <= n; i++)
    if (!mark[i]) {
      for (int j = i * i; j <= n; j += i)
        mark[j] = 1;
    }
  int res = 0;
  for (int i = 2; i <= n; i++)
    if (!mark[i])
      res++;
  printf("%d\n", res);
  return 0;
}