#include <cmath>
#include <iomanip>
#include <iostream>
#include <math.h>
#include <vector>
#include <tuple>
#include <set>
#include <map>

using namespace std;

using ll = long long;
const ll INFLL = 1e18;
const ll MOD = 1e9 + 7;

struct Comb {
  ll n, k;
  map<ll,ll> cache;

  Comb(ll _n, ll _k): n(_n), k(_k) {
    build();
  }

  void build() {
    ll b = 1;
    ll p = 1;

    for (ll i = 0; i < k; ++i) {
      b *= (n + k - 1 - i);
      b %= MOD;

      p *= i + 1;
      p %= MOD;
    }

    b = (b * modpow(p, MOD - 2)) % MOD;
    cache[n + k - 1] = b;

    for (ll i = n - 1; i >= 1; --i) {
      b = (b * i) % MOD * modpow(i + k, MOD - 2) % MOD;
      cache[i + k - 1] = b;
    }
  }

  ll get(ll n, ll x) {
    // cout << n - x + k << " " << x + k - 1 << endl;
    return (cache[n - x + k] * cache[x + k - 1]) % MOD;
  }

  ll modpow(ll a, ll n) {
    if (n == 0) return 1;
    if (n % 2) return a * modpow(a, n - 1) % MOD;
    ll t = modpow(a, n / 2);
    return (t * t) % MOD;
  }

};

int main() {
  ll n, k;
  cin >> n >> k;

  Comb com(n, k);
  vector<ll> T(n + 1);

  for (int i = 1; i <= n; ++i) {
    T[i] = com.get(n, i);
  }

  vector<ll> a(n + 1);
  for (int i = 1; i <= n; ++i) cin >> a[i];

  ll sum = 0;
  for (int i = 1; i <= n; ++i) {
    sum += (a[i] * T[i]) % MOD;
    sum %= MOD;
  }

  cout << sum << endl;
  return 0;
}