N, K = map(int, input().split())
A = list(map(int, input().split()))

m = 1000000007

if K == 0:
    result = 0
    for a in A:
        result += a
        result %= m
    print(result)
else:
    result = 0
    for i in range(N):
        result += A[i] * (i * (N - i) + (N - i))
        result %= m
    print(result)