#include <stdio.h>
#define dim 2000004
char ciur[dim];
int i, j, k, n;
int main(void)
{
 freopen("ciur.in","r",stdin);
 freopen("ciur.out","w",stdout);
 scanf("%d", &n);
 for ( i = 2; i <= n; i++)
  ciur[i] = 1;

 for(i = 2; i <= n; i++)
  if(ciur[i])
	for(j = 2; j <= n/i; j++)
	 ciur[ i*j ] = 0;
 for(i = 2; i <= n; i++)
  if(ciur[i])
	k++;

 printf("%d\n",k);
 fcloseall();
 return 0;
}