mod = 10 ** 9 + 7
N, K = map(int, input().split())
A = list(map(int, input().split()))

L = [1] * (N + 1)
for i in range(1, N + 1):
    L[i] = L[i - 1] * (K + i) * pow(i, mod - 2, mod) % mod
R = L[::-1]


ans = 0
for i, a in enumerate(A):
    ans += a * L[i] * R[i + 1] % mod
    if ans >= mod:
        ans -= mod

print(ans)