990+891+792+693+594+495+396+297+198+99 (use two different simple methods to answer, there must be a necessary process)
990+891+792+693+594+495+396+297+198+99(用两种不同的简便方法解答，要有必要的过程)
<gadget id="calculator">990 + 891 + 792 + 693 + 594 + 495 + 396 + 297 + 198 + 99</gadget>
<output>5_445</output>

<result>5_445</result>