program ciurul_lui_erathostenes;
var n,i,k,j:longint;
	a:array[1..200000000] of 0..1;		//1 - nu-i prim
	f,g:text;							//0 - e prim

BEGIN

	assign(f,'ciur.in');reset(f);
	read(f,n);
	close(f);

	for i:=2 to n div 2 do
	  for j:=2 to n div 2 do
	    a[i*j]:=1;

	for i:=2 to n do
	  if a[i]=0 then inc(k);

	assign(g,'ciur.out');rewrite(g);
	write(g,k);
	close(g);

END.