A snail is at the bottom of a well 15 meters deep. If it climbs up 3 meters during the day and slides down 1 meter at night, how many days can the snail climb out of the well?
一只蜗牛在一口15米深的井底，如果他每天白天往上爬3米，但是在晚上又往下滑1米，这只蜗牛几天能爬出这口井？
<gadget id="calculator">15 - 3</gadget>
<output>12</output>

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

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>