n, k = map(int, input().split())
mo = 10 ** 9 + 7
a, b = 1, 1
for _ in range(n):
    a = (a * k + a * (1 + k) * k // 2) % mo
    b = (b * (1 + k) * k // 2) % mo
print((a - b) % mo)