snail climbs up from the bottom of the well, climbs at night, sleeps during the day, climbs 4 feet every night, and slides down 2 feet during the day, the well is 10 feet deep, how many days does it take to come out.
一只蜗牛从井底往上爬，晚上爬，白天睡觉，每天晚上爬4尺，白天又会滑下去2尺，井深10尺，它要多少天能出来．
<gadget id="calculator">10 - 4</gadget>
<output>6</output>

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

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>