Given a tree of $n$ nodes, your task is to count the number of distinct paths that consist of exactly $k$ edges.
The first input line contains two integers $n$ and $k$ : the number of nodes and the path length. 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 $b$ .
Print one integer: the number of paths.