#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+=2)
	       if (i%x==0) { ok=0; break; }
	    if (ok==1) k++;
	  }
	g<<k;
	return 0;
}