Fixed-Length Paths II

Given a tree of n nodes, your task is to count the number of distinct paths that have at least k_1 and at most k_2 edges. Input The first input line contains three integers n, k_1 and k_2: the number of nodes and the path lengths. The nodes are numbered 1,2,\ldots,n. Then there are n-1 lines describing the edges. Each line contains two integers a and b: there is an edge between nodes a and b.