Power Sum
Compute ∑i=1..N iK modulo 109+7.
Input: one line with two integers N and K.
Output: the power sum mod 109+7.
Constraints:
- 1 ≤ N ≤ 1018
- 0 ≤ K ≤ 100
Sample Tests
Input 1
3 2
Output 1
14
Input 2
5 0
Output 2
5
Discussion (opens after you solve — no spoilers before)
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