program erathostenes;
var i,j,n,x,nr:longint;
    v:array[1..2000002] of 0..1;
    f,g:text;
begin
assign(f,'ciur.in'); assign(g,'ciur.out');
reset(f); rewrite(g);
readln(f,n);
for i:=2 to n do
 if v[i]=0 then
 begin
  nr:=nr+1;
  for j:=2 to n div i do
   v[i*j]:=1;
  end;
 write(g,nr);
close(f); close(g);
end.