def inv(x):
    return pow(x, MOD-2, MOD)
    
N, K = map(int, input().split())
A = list(map(int, input().split()))
MOD = 10**9+7
C = [1]*N

for i in range(1, N):
    C[i] = C[i-1]*(K+i)*inv(i)

ans = 0

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

print(ans)