#include <fstream.h>
int main ()
{	int x,n,i,ok=1,k=1;
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	f>>n;
	for (i=3; i<=n; i+=2)
	 {  ok=1;
	    for (x=3;x*x<=i;x=x+2)
	       if (i%x==0) ok=0;
	    if (ok==1) k++;
	 }
	 g<<k;
	 return 0;
}