There is a snail that wants to climb to the top of a 15-meter-high tree. It can climb up to 4.17 meters during the day, but it has to slide down 3.17 meters at night when it sleeps. How many days does it take for this snail to climb to the top of the tree?
有一只蜗牛要爬到一棵高15米的树顶上，它每天白天能爬上4.17米，但到了晚上睡觉时又要滑下3.17米，这只蜗牛几天后才能爬上树顶？
<result>12</result>