#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

const ll MOD = 1000000007;
vector<ll> A;

ll mod_pow(ll x, ll n, ll mod = MOD) {
  ll res = 1;

  while (n > 0) {
    if (n & 1) {
      res = res * x % mod;
    }

    x = x * x % mod;
    n >>= 1;
  }

  return res;
}

ll mod_inverse(ll x, ll mod = MOD) {
  return mod_pow(x, mod - 2, mod);
}

ll build_key(ll n, ll k) {
  return n * 100000000 + k;
}

ll comb(ll n, ll k, map<ll, ll> &memo) {
  memo[k] = 1;
  ll a = 1;
  ll b = 1;
  ll len = n - k;
  for (ll i = 1; i <= len; ++i) {
    a *= (k + i);
    a %= MOD;
    b *= i;
    b %= MOD;
    memo[k + i] = a * mod_inverse(b, MOD) % MOD;
  }

  return b * mod_inverse(a, MOD) % MOD;
}

int main() {
  ll N, K;
  cin >> N >> K;
  A.resize(N);

  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  map<ll, ll> memo;
  ll ans = 0;
  comb(K + N, K, memo);

  for (ll i = 1; i <= N; ++i) {
    ll a = A[i - 1];
    ll b = a * memo[K + i - 1] % MOD;
    ll c = b * memo[N - i + K] % MOD;
    ans += c;
    ans %= MOD;
  }

  cout << ans << endl;

  return 0;
}