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

mod = 10**9+7
inv = [0]*(N+1)
inv[0] = 1
for i in range(1,N):
    inv[i] = (inv[i-1]*pow(i,mod-2,mod))%mod
comb = [0]*N
comb[0] = 1
for i in range(1,N):
    comb[i] = (comb[i-1]*(K+i))%mod

res = 0
for i in range(1,N+1):
    res += (A[i-1]*comb[i-1]*inv[i-1]*comb[N-i]*inv[N-i])%mod
    res %= mod
print(res)