N, K = map(int, input().split())
A = tuple(map(int, input().split()))
MOD = 10 ** 9 + 7
modinv = lambda a, mod=MOD: pow(a, mod - 2, mod)

comb = [1] * N
for i in range(1, N):
    tmp = (i + K) * modinv(i) % MOD
    comb[i] = comb[i - 1] * tmp % MOD

ans = 0
for i, a in enumerate(A):
    tmp = comb[i] * comb[N - i - 1] % MOD
    ans += a * tmp % MOD
    ans %= MOD
print(ans)