n, k = map(int, input().split())
a = list(map(int, input().split()))
MOD = 10 ** 9 + 7
comb = Combination(10 ** 6, MOD)


ball = k
dp = [0] * (n + 10)
dp[0] = 1
for i in range(n + 9):
    dp[i + 1] = dp[i] * (ball + i + 1) * pow(i + 1, MOD - 2, MOD)
    dp[i + 1] %= MOD


ball = k
ans = 0
for i in range(n):
    tmp = 1
    box = n - i
    tmp *= dp[box - 1]
    box = i + 1
    tmp *= dp[box - 1]
    ans += a[i] * tmp % MOD
    ans %= MOD
print(ans % MOD)