import sys
input = sys.stdin.readline
from collections import *

def inv(x):
    return pow(x, MOD-2, MOD)

N, K = map(int, input().split())
A = list(map(int, input().split()))
fact = [0]*N
fact[0] = 1
MOD = 10**9+7

for i in range(1, N):
    fact[i] = fact[i-1]*i%MOD
    
ans = 0
l = 1
r = 1

for i in range(1, N):
    r *= K+i
    r %= MOD

for i in range(N):
    ans += A[i]*l*inv(fact[i])*r*inv(fact[N-1-i])
    ans %= MOD
    l *= K+i+1
    l %= MOD
    r *= inv(K+N-1-i)
    r %= MOD

print(ans)