How to make a round window

procedure TForm1.FormCreate(Sender: TObject);
var
  R: HRgn;
  a: integer;
begin
  a      := -25;
  Height := 500;
  Width  := 550;
  R      := CreateEllipticRgn(-a, - a, Width - 45, Height - 45);
  SetWindowRgn(Handle, R, True);
end;