The little monkey Wangwang wants to climb up the 18-meter-high tree, but it will slide down 2 meters after climbing up to 4 meters, and then muster up the courage to climb the second time... How many times can the little monkey Wangwang climb to the top of the tree?
小猴汪汪要爬上18米高的大树，可它爬上4米后就会滑下2米，然后又鼓足勇气爬第二次…，小猴汪汪第多少次才能爬上树顶．
<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<result>8</result>