#include<fstream.h>
long n,ind=2,cont=0;
char a[2000002];
int verif();
int main()
{
  long var;

  ifstream f("ciur.in");
  f>>n;
  f.close();

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

	for(int i=0;i<cont&&ok;i++)
	if(ind%a[i]==0)ok=0;

	return ok;
}