#include <iostream>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <cstdlib>
#include <map>
#include <set>
#include <queue>
#include <vector>
using namespace std;
#define MOD 1000000007

long long modinv(long long a, long long mod) {
    long long b = mod, u = 1, v = 0;
    while (b) {
        long long t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= mod;
    if (u < 0) u += mod;
    return u;
}

int main() {
    long long N, M; cin >> N >> M;
    vector<long long> A(N);
    for (int i = 0; i < N; i++) cin >> A[i];
    long long ans = 0;
    long long com = 0;
    for (long long i = N - 1; i >= 0; i--) {
        if (i == N - 1) com = M % MOD;
        else com = (com * ((N - i + M - 1) % MOD) % MOD) * modinv(N - i, MOD) % MOD;
        ans += A[i] * com % MOD;
    }
    cout << ans % MOD << endl;
}