#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

const long long MOD = 1e9 + 7;

vector<long long> f, g;

long long homo(int n, int r) {
  // homo(n, r) = comb(n+r-1, r) = comb(r+n-1, n-1)
  return f[n-1] * g[n-1] % MOD;
}

long long modpow(long long x, long long p, long long mod) {
  long long ret = 1;
  while (p) {
    if (p & 1)
      ret = ret * x % mod;
    x = x * x % mod;
    p >>= 1;
  }
  return ret;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, k;
  cin >> n >> k;
  vector<long long> a(n);
  REP (i, n) cin >> a[i];

  f.resize(n);
  f[0] = 1;
  for (int i = 1; i < n; i++)
    f[i] = f[i-1] * (k+i) % MOD;
  
  g.resize(n);
  g[0] = 1;
  for (int i = 1; i < n; i++)
    g[i] = g[i-1] * i % MOD;
  for (int i = 1; i < n; i++)
    g[i] = modpow(g[i], MOD-2, MOD);

  long long ret = 0;
  REP (i, n) {
    long long pat = homo(i+1, k) * homo(n-i, k) % MOD;
    ret += pat * a[i] % MOD;
    ret %= MOD;
  }

  cout << ret << endl;
  
  return 0;
}