#include <cstdio>

#define MAX_N 2000010

using namespace std;

int n, np;
char prime[MAX_N];

int main() {

  freopen("ciur.in", "r", stdin);
  freopen("ciur.out", "w", stdout);

  scanf("%d", &n);

  np = 1;
  for(int i = 3; i <= n; i += 2)
    if(prime[i] == 0) {
      np ++;
      for(int j = i * i; j <= n && j > 0; j += 2 * i)
	prime[j] = 1;
    }

  printf("%d\n", np);

  return 0;
}