There is a well 7 meters deep, and a snail climbs up from the bottom of the well. Climb 3 meters during the day and fall 2 meters at night. How many days does it take for a snail to crawl out of a well?
有口井7米深，有个蜗牛从井底往上爬．白天爬3米，晚上往下坠2米．问蜗牛几天能从井里爬出来？
<gadget id="calculator">7 - 3</gadget>
<output>4</output>

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

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

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

<result>5</result>