MOD = 10**9 + 7
n, k = map(int, input().split())
comb = [1 for _ in range(n+1)]
for i in range(1, n):
	comb[i] = comb[i-1] * (k+i) * pow(i, MOD-2, MOD)
	comb[i] %= MOD

a = list(map(int, input().split()))
ans = 0
for i, x in enumerate(a):
	j = n-i-1
	ans += comb[i] * comb[j] * x
	ans %= MOD
print(ans)