#include<fstream.h>

long c,n,a,d,b,nr;
char v[1000000],gasit;

int main()
{
 ifstream f("ciur.in");
 ofstream g("ciur.out");
 f>>n;
 nr=1;
 d=3;
 while(d<=n)
  {
   a=d*d;b=(d<<1);nr++;
   while(a<=n){c=(a>>1);if(!v[c])v[c]=1;a+=b;}
   gasit=0;c=(d>>1)+1;
   while(!gasit)
   {
    if(!v[c]){d=(c<<1)+1;gasit=1;}
    else c++;
    }
   }
 g<<nr;
 return 0;
 }