snail climbs up from the bottom of a well that is 13 meters deep. It climbs 3 meters during the day and slides down 2 meters at night. How many days does it take for the snail to climb out of the well?
一只蜗牛从深13米的井底往上爬，它白天爬3米，晚上下滑2米，这只蜗牛多少天能爬出井口．
<gadget id="calculator">13 - 3</gadget>
<output>10</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">10 / 1</gadget>
<output>10</output>

<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<result>11</result>