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