#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

constexpr int P = 1000000007;

ll modinv(int n) {
    int m = P, y = 0, v = 1;
    while (1) {
        int q = m / n;
        int r = m % n;
        if (r == 0) return v < 0 ? v + P : v;
        y -= v * q;
        swap(y, v);
        m = n;
        n = r;
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, k;
    cin >> n >> k;

    vector<int> a(n);
    ll s = 0;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        s += a[i];
    }
    s %= P;

    ll r = 0, x = 0, t = 1, v = 0;
    vector<int> u(n);
    u[0] = 1;
    for (int i = 1; i < n; i++) {
        u[i] = (ll)u[i - 1] * modinv(i) % P * (k + i) % P;
    }
    for (int i = 0; i < n; i++) {
        if (i > 0) t = t * modinv(i) % P * (k - 1 + i) % P;
        ll y = t * u[n - 1 - i] % P;
        r -= y * v % P;
        x += y;
        v += a[i] + a[n - 1 - i]; v %= P;
    }
    x %= P;

    r += s * x;
    r %= P;
    if (r < 0) r += P;

    cout << r << endl;

    return 0;
}