MOD = 10 ** 9 + 7

n, k = map(int, input().split())
A = list(map(int, input().split()))
nHk = [0] * (n + 1)
x = 1
for i in range(1, n + 1):
    nHk[i] = x
    x *= (k + i)
    x %= MOD
    x *= pow(i, MOD - 2, MOD)
    x %= MOD

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