#include<stdio.h>
int main()
{int n,i,j,u,nr=0,a[100000];
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n);
if(n>=2)
	nr++;
for(i=3;i<=n;i+=2)
a[i]=i;
for(i=3;i<=n;i+=2)
{if(a[i]!=0)
   {nr++;
    for(j=i*2;j<=n;j+=i)
		a[j]=0;
   }
}
printf("%d",nr);
return 0;}