n, k = map(int, input().split())
A = list(map(int, input().split()))

mod = 10**9+7

N = 2*10*5+50
C = [0]*N
C[0] = 1
for i in range(1, N):
    C[i] = C[i-1]*(k+i)*pow(i, mod-2, mod)
    C[i] %= mod

def cmb(i):
    return C[i]

ans = 0
for i, a in enumerate(A):
    ans += a*cmb(i)*cmb(n-i-1)
    ans %= mod
print(ans)