#include<stdio.h>
char p[2000010];
int main()
{
 freopen("ciur.in","r",stdin);
 freopen("ciur.out","w",stdout);
 int i,j;
 int n=0,t=0; 
 scanf("%d",&n);
 
 for(i=2;i<=n;i++)
    if(!p[i])
	{ t++;
	
	 for(j=2*i;j<=n;j+=i)
		p[j]=1;  
	}
	printf("%d\n",t);
 return 0;
}