codeforces#P622F. The Sum of the k-th Powers
The Sum of the k-th Powers
Description
There are well-known formulas: 
, 
, 
. Also mathematicians found similar formulas for higher degrees.
Find the value of the sum 
modulo 109 + 7 (so you should find the remainder after dividing the answer by the value 109 + 7).
The only line contains two integers n, k (1 ≤ n ≤ 109, 0 ≤ k ≤ 106).
Print the only integer a — the remainder after dividing the value of the sum by the value 109 + 7.
Input
The only line contains two integers n, k (1 ≤ n ≤ 109, 0 ≤ k ≤ 106).
Output
Print the only integer a — the remainder after dividing the value of the sum by the value 109 + 7.
Samples
4 1
10
4 2
30
4 3
100
4 0
4