#include<stdio.h>
char v[2000005];      
int main()      
{long n,i,j,m=0;      
     
freopen("ciur.in","r",stdin);      
freopen("ciur.out","w",stdout);      
scanf(" %ld",&n);      
     
for(i=2;i<=n;++i)if(!v[i]){++m;for(j=i+i;j<=n;j+=i)v[j]=1;}      
j=0;      
printf("%ld\n",m);      
       
     
return 0;      
}