#include <stdio.h>
int main()
{ char ok[2000000];
  long int n,i,j,nr;
  
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
  scanf("%ld",&n);
  for (i=2;i<=n;i++) ok[i]=0;nr=0;
  for (i=2;i<=n;i++) 
	if (!ok[i]) {nr++; for (j=1;j<=n/2;j++) ok[i*j]=1;}  
 printf("%ld",nr);

return 0;}