N,K = map(int, input().split())
A = [int(a) for a in input().split()]

mod = 10**9+7

cmb = [0]*(N+1)
cmb[0] = 1
num = 1
den = 1
for i in range(1, N+1):
    num *= (i+K)
    den *= i
    num %= mod
    den %= mod
    cmb[i] = num*pow(den, mod-2, mod)%mod



ans = 0
for i in range(N):
    ans += A[i] * cmb[i] * cmb[N-i-1] % mod
    ans %= mod

print(ans)