#include<stdio.h>
int n,nr,i,j;
bool a[2000001];
int main()
{
 freopen("ciur.in","rt",stdin);
 freopen("ciur.out","wt",stdout);
 scanf("%d",&n);
 for(i=2;i<=n;i++)
	if(!a[i]) 
		{
		 nr++;
		 for(j=i+i;j<=n;j+=i) a[j]=1;
		}
 printf("%d",nr);
 return 0;
}