"""
愚直解
from collections import defaultdict


def solve(ans, cnt):
    if cnt == k:
        return
    n = len(ans)
    for l in range(n):
        for r in range(l + 1, n + 1):
            if cnt == k - 1:
                memo[len(ans[l:r])] += 1
            solve(ans[l:r], cnt + 1)
    

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

memo = defaultdict(int)
ans = [1, 2, 3, 4, 5, 6]
k = 4
solve(ans, 0)
print(memo)
"""


class Combination:
    """階乗とその逆元のテーブルをO(N)で事前作成し、組み合わせの計算をO(1)で行う"""
    def __init__(self, n, MOD):
        self.fact = [1]
        for i in range(1, n + 1):
            self.fact.append(self.fact[-1] * i % MOD)
        self.inv_fact = [0] * (n + 1)
        self.inv_fact[n] = pow(self.fact[n], MOD - 2, MOD)
        for i in reversed(range(n)):
            self.inv_fact[i] = self.inv_fact[i + 1] * (i + 1) % MOD
        self.MOD = MOD

    def inverse(self, k):
        """kの逆元を求める O(1)"""
        return (self.inv_fact[k] * self.fact[k - 1]) % self.MOD

    def factorial(self, k):
        """k!を求める O(1)"""
        return self.fact[k]

    def inverse_factorial(self, k):
        """k!の逆元を求める O(1)"""
        return self.inv_fact[k]

    def permutation(self, k, r):
        """kPrを求める O(1)"""
        if k < r:
            return 0
        return (self.fact[k] * self.inv_fact[k - r]) % self.MOD

    def combination(self, k, r):
        """kCrを求める O(1)"""
        if k < r:
            return 0
        return (self.fact[k] * self.inv_fact[k - r] * self.inv_fact[r]) % self.MOD

    def combination2(self, k, r):
        """kCrを求める O(r)
        kが大きいが、r <= nを満たしているときに使用
        """
        if k < r:
            return 0
        res = 1
        for l in range(r):
            res *= (k - l)
            res %= self.MOD
        return (res * self.inv_fact[r]) % self.MOD


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)