#include <iostream>
#include <vector>

const long long mod = 1000000007;
using ll = long long;

long long modpow(long long n, long long k, long long m)
{
    long long res = 1;
    while (k > 0)
    {
        if (k & 1)
            res = res * n % m;
        k = k >> 1;
        n = n * n % m;
    }
    return res;
}

int main()
{
    ll n, k;
    std::cin >> n >> k;
    std::vector<ll> A(n);
    for (int i = 0; i < n; i++)
        std::cin >> A.at(i);
    ll ans = 0, c = 1, f = 1;
    for (ll i = 1; i < n + k; i++)
    {
        f = (f * i) % mod;
        if (i == k)
            c = (c * modpow(f, mod - 2, mod)) % mod;
        if (i == n - 1)
            c = (c * modpow(f, mod - 2, mod)) % mod;
        if (i == n - 1 + k)
            c = c * f % mod;
    }
    for (ll i = 0; i < n; i++)
    {
        ll a = A.at(i);
        ans = (ans + a * c % mod)%mod;
        c = c * (k + i + 1) % mod * (n - i - 1) % mod;
        c = c * modpow((i + 1) * (n - 1 - i + k) % mod, mod - 2, mod) % mod;
    }
    std::cout << ans << std::endl;
}