#include <stdio.h>
#include <string.h>
#include <math.h>


int main ()
{
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
    
  long k,n,i,j;

  unsigned char p[2000001];
  scanf("%ld", &n);
  
  memset(p,'1',2000001);
  i=2; k=0;
  while (i<=n)
  if (p[i]=='1'){
	              for( j=i;j<=n;j=j+i)
	               p[j]='0';
	               k++;
	               }
	   else i++;
      
  printf("%ld", k);
  
  return 0;

}