There is a snail that wants to climb from the ground to a tree with a height of 11.5m. It can climb 3.5m during the day, but slides down 1.5m every night. How many days does it take for the snail to climb to the top of the tree?
有一只蜗牛要从地面爬到一颗高11.5m的树上，它白天能爬3.5m，但是每到晚上又下滑1.5m，这只蜗牛第几天才能爬到树顶？
<gadget id="calculator">11.5 - 3.5</gadget>
<output>8</output>

<gadget id="calculator">3.5 - 1.5</gadget>
<output>2</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>