#include<fstream.h>
#include<math.h>

unsigned long n,c,i;
unsigned int d,ok;

int prim(int);

main()
{
	ifstream In("ciur.in");
	ofstream Out("ciur.out");
	In>>n;
	In.close();
	for(i=2;i<=n;i++)
	   if(prim(i)) c++;

	Out<<c<<'\n';
	Out.close();
	return 0;
}

int prim(int x)
{
	ok=1;
	for(d=2;d<=sqrt(n);d++)
	{
	     if(x%d==0) {ok=0;break;}
	}
	return ok;
}