#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define REP(i,m,n) for(int i=(int)(m); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define RREP(i,m,n) for(int i=(int)(m); i>=(int)(n); i--)
#define rrep(i,n) RREP(i,n-1,0)
#define all(v) v.begin(), v.end()
const int inf = 1e9+7;
const ll longinf = 1LL<<60;
const ll mod = 1e9+7;

ll modpow(ll a, ll N) {
  ll ans = 1;
  ll tmp = a;
  while(N > 0) {
    if(N % 2 == 1) (ans *= tmp) %= mod;
    (tmp *= tmp) %= mod;
    N /= 2;
  }
  return ans;
}
ll modinv(ll a, ll m=mod) {
  ll b = m, u = 1, v = 0;
  while(b) {
    ll t = a / b;
    a -= t * b; swap(a, b);
    u -= t * v; swap(u, v);
  }
  u %= m;
  if(u < 0) u += m;
  return u;
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n; ll k; cin >> n >> k;
  vector<ll> A(n); rep(i, n) cin >> A[i];
  ll ans = 0;
  vector<ll> comb(n);
  comb[0] = 1;
  for(int i=1; i<n; i++) {
    comb[i] = comb[i-1] * (k+i) %  mod * modinv(i) % mod;
  }
  rep(i, n) {
    (ans += A[i] * comb[i] % mod * comb[n-1-i] % mod) %= mod;
  }
  cout << ans << "\n";
  return 0;
}