mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    # comb init
    # mod = 1000000007
    nmax = 2 * 10 ** 5 + 10  # change here
    fac = [0] * nmax
    finv = [0] * nmax
    inv = [0] * nmax
    fac[0] = 1
    fac[1] = 1
    finv[0] = 1
    finv[1] = 1
    inv[1] = 1
    for i in range(2, nmax):
        fac[i] = fac[i - 1] * i % mod
        inv[i] = mod - inv[mod % i] * (mod // i) % mod
        finv[i] = finv[i - 1] * inv[i] % mod

    def comb(n, r):
        if n < r:
            return 0
        else:
            return (fac[n] * ((finv[r] * finv[n - r]) % mod)) % mod

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

    facK = {K+1: K+1}
    for i in range(2, N*2):
        facK[K+i] = (facK[K+i-1] * (K+i))%mod

    ans = 0
    for i, a in enumerate(A):
        if i == 0:
            l = 1
        else:
            l = (facK[i+1 + K - 1] * finv[i])%mod
        if i == N-1:
            r = 1
        else:
            r = (facK[N-i + K - 1] * finv[N-i-1])%mod
        ans = (ans + ((a * l)%mod * r)%mod)%mod
    print(ans)


if __name__ == '__main__':
    main()