A hole is 11 meters deep. A snail is struggling to climb up from the bottom of the hole. It can climb up to 3 meters during the day, but at night it not only cannot climb up, but also slides down 1 meter. How many days can the snail climb to the entrance of the hole?
一个洞有11米深，一只蜗牛在洞底下拼力向上爬，白天能爬上3米，到晚上不但不能往上爬，还要滑下1米，这只蜗牛多少天能爬到洞口．
<gadget id="calculator">11 - 3</gadget>
<output>8</output>

<gadget id="calculator">3 - 1</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>