"Add 20 and subtract 50" from 2100, this is called one operation, after how many operations the result is 0.
从2100里"加上20，减去50"，这称作是一次操作，经过多少次操作所得的结果是0．
<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">2_100 / 30</gadget>
<output>70</output>

<result>70</result>