A snail climbs up from the bottom of a well 10 meters deep. It climbs 3 meters during the day and slides down 2 meters at night. Crawling like this, how many days can it climb to the mouth of the well?
一只蜗牛从10米深的井底向上爬，它白天爬3米，晚上滑下2米．照这样子爬行，它多少天能够爬到井口呢？
<gadget id="calculator">3 / 3</gadget>
<output>1</output>

<gadget id="calculator">10 - 1 - 2</gadget>
<output>7</output>

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

<gadget id="calculator">7 + 1</gadget>
<output>8</output>

<result>8</result>