#include<fstream.h>
int main()
{
  long n,ind=2,var,cont=0;
  int a[20000];
  ifstream f("ciur.in");
  f>>n;
  f.close();

  while(ind<=n)
  {  cont++;
	 var=ind*2;
	 while(var<=n)
	 {
		a[var]=-1;
		var+=ind;
	 }
	 do
	 {
	   ind++;
	 }while(a[ind]==-1);
  }
  ofstream g("ciur.out");
  g<<cont;
  g.close();
  return 0;
}