#include <stdio.h>
#define dim 2000004
char ciur[dim];
int n,k,i,j;
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;
}