#include<fstream.h>
#define fin "ciur.in"
#define fout "ciur.out"

int main()

{ long n;
  int a,b,c,k=0,ok=0;
  ifstream in(fin);
  in>>n;
  for (a=3;a<=n;a+=2)
	{ for (b=2; b<=a/2; b++)
	    ok=0;
	  { if (a%b==0) {ok=1; break;} }
	    if (ok==0) k++;
	    else continue;
        }
  ofstream out(fout);
  out<<k;
  in.close ();
  out.close();

  return 0;
}