N,K = map(int,input().split())
A = list(map(int,input().split()))
P = 10 ** 9 + 7
C = N + 5
fact = [1] * C
fact_inv = [1] * C
factk = [1] * C
factk[1] = K + 1
for i in range(2,C):
    fact[i] = fact[i-1] * i % P
    factk[i] = factk[i-1] * (K + i) % P
fact_inv[-1] = pow(fact[-1],P-2,P)
for i in range(C-2,0,-1):
    fact_inv[i] = fact_inv[i+1] * (i + 1) % P
def comb(x):
    return factk[x-1] * fact_inv[x-1] % P
ans = 0
for i in range(N):
    tmp = A[i] * comb(i+1) % P * comb(N-i) % P
    ans = (ans + tmp)% P
print(ans)