program ciur;
var f,g:text;
    n,i,k:integer;

function prim(nr:integer):boolean;
  var i:byte;
  begin
  prim:=true;
  for i:=2 to nr div 2 do
    if nr mod i=0 then prim:=false;
  end;

begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);rewrite(g);
readln(f,n);
k:=0;
for i:=2 to n do
 if prim(i) then inc(k);
write(g,k);
close(f);
close(g);
end.