There is a snail that wants to climb to the top of a tree with a height of 16m. It can climb 4.17m every day during the day, but at night, it slides down 2.17m in sleep. How many days will it take for this snail to climb to the top of the tree?
有一只蜗牛要爬到一棵高16m的树顶上，它每天白天能爬上4.17m，但到了晚上，在睡梦中又要滑下2.17m，这只蜗牛几天后才能爬上树顶？
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