There is a well 10 meters deep, and a snail climbs up from the bottom of the well. Because the well wall is slippery, the snail climbs 2 meters during the day and slides down 1 meter at night. How many days does it take for the snail to climb up?
有一口10米深的水井，一只蜗牛从井底向上爬．因为井壁滑，蜗牛白天爬2米，晚上向下滑1米，这只蜗牛多少天可以爬上来．
<gadget id="calculator">10 - 2</gadget>
<output>8</output>

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

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

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>