#include<stdio.h>
long n;
int c[2000001];

void ciur()
{
long i,j;
for(i=1;2*i+1<=n;++i)
   if(c[i]==0)
     for(j=2*i*i+2*i;j<=n;++j)
         c[j]=1;
}

int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);

scanf("%ld",&n);
long i,num=0;
ciur();
n=n/2;
for(i=0;i<n;++i)
   if(c[i]==0)
     ++num;

printf("%ld\n",num);

return 0;
}