CF641G Little Artem and Graph

Little Artem is given a graph, constructed as follows: start with some $ k $ -clique, then add new vertices one by one, connecting them to $ k $ already existing vertices that form a $ k $ -clique. Artem wants to count the number of spanning trees in this graph modulo $ 10^{9}+7 $ .

First line of the input contains two integers $ n $ and $ k $ ( $ 1

Output a single integer — the number of spanning trees in the given graph modulo $ 10^{9}+7 $ .