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

# (K+a)Caの計算
F = [0] * (N + 1)
F[0] = 1
for i in range(1, N + 1):
    F[i] = (K + i) * pow(i, MOD - 2, MOD) * F[i - 1]
    F[i] %= MOD

ans = 0
for i in range(N):
    ans += F[i] * F[N - i - 1] * A[i]
    ans %= MOD

print(ans)