CF461B Appleman and Tree

Appleman has a tree with $ n $ vertices. Some of the vertices (at least one) are colored black and other vertices are colored white. Consider a set consisting of $ k $ $ (0

The first line contains an integer $ n $ ( $ 2

Output a single integer — the number of ways to split the tree modulo $ 1000000007 $ ( $ 10^{9}+7 $ ).