99+99*99+99*99*99=how much.
99+99*99+99*99*99=多少．
<gadget id="calculator">99 * 99</gadget>
<output>9_801</output>

<gadget id="calculator">99 * 99 * 99</gadget>
<output>970_299</output>

<gadget id="calculator">99 + 9_801 + 970_299</gadget>
<output>980_199</output>

<result>980_199</result>