#include<fstream.h>
#include<math.h>
ifstream in("ciur.in");
ofstream out("ciur.out");
int main()
{int N,i,d,nr=0,prim;
in>>N;
for(i=2;i<=N;i++)
 {prim=1;
  for(d=2;d<=sqrt(i);d++)
   if(i%d==0)
    prim=0;
  if(prim==1)
   nr++;
  }
out<<nr;
in.close();
out.close();
return 0;
}