#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
#define debug(x) std::cout << #x << ": " << x << '\n';

const int MOD = 1000 * 1000 * 1000 + 7;

int mod(int n) {
    n %= MOD;
    if (n < 0) return n + MOD;
    else return n;
}   
int fp(int a, int p) {
    int ans = 1, c = a;
    for (int i = 0; (1ll << i) <= p; ++i) {
        if ((p >> i) & 1) ans = mod(ans * c);
        c = mod(c * c);
    }   
    return ans;
}   
int dv(int a, int b) { return mod(a * fp(b, MOD - 2)); }

int C(int n, int k) {
    int ans = 1;
    for (int i = 1; i <= n; ++i)
        ans = mod(ans * i);
    int d = 1;
    for (int i = 1; i <= n - k; ++i)
        d = mod(d * i);
    for (int i = 1; i <= k; ++i)
        d = mod(d * i);
    return dv(ans, d);
}   

signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif

    int n, k;
    cin >> n >> k;
    vector <int> a(n);
    for (int i = 0; i < n; ++i)
        cin >> a[i];

    if (k == 0) {
        int sum = 0;
        for (int i = 0; i < n; ++i)
            sum = mod(sum + a[i]);
        cout << sum << endl;
        exit(0);
    }   

    int ans = 0;

    int lf = fp(k, MOD - 2);
    int rf = C(n + k, k);
    for (int i = 0; i < n; ++i) {
        int l = i + 1;
        int r = n - i;

        lf = mod(lf * (l + k - 1));
        if (l > 1) {
            lf = dv(lf, l - 1);
        }

        rf = dv(rf, r + k);
        rf = mod(rf * r);

        ans = mod(ans + mod(lf * rf) * a[i]);
        // C(l + k - 1, k) * C(r + k - 1, k)
    }   

    cout << ans << endl;
}