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