#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
typedef long long ll;
#define MOD 1000000007
using namespace std;
#define MAX 1000000
ll fac[MAX], finv[MAX], inv[MAX];
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAX; i++) {
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
ll COM(ll n, ll k) {
    if(n < k)
        return 0;
    if(n < 0 || k < 0)
        return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
int main() {
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n + 1);
    for(int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    ll ans = 0;
    COMinit();
    for(int i = 1; i <= n; i++) {
        ans += a[i] * ((COM(k + i - 1, i - 1) * COM(k + n - i, n - i)) % MOD) %
               MOD;
        ans %= MOD;
    }
    cout << ans << endl;
}