Subtract 15 from 100, add 10, then subtract 15, add 10, ..., continue in this way, when the result is 0, how many 15 should be subtracted at least.
从100里减去15，再加上10，然后15减去，加上10，…，这样连续进行，当得数是0时，最少减去多少个15．
<gadget id="calculator">100 - 15</gadget>
<output>85</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<gadget id="calculator">85 / 5</gadget>
<output>17</output>

<gadget id="calculator">17 + 1</gadget>
<output>18</output>

<result>18</result>