#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;

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];

  vector<long long> comb(n);  // comb(i) = C(k+i, k)
  comb[0] = 1;
  for (int i = 1; i < n; i++)
    comb[i] = comb[i-1] * (k + i) % MOD * modpow(i, MOD-2, MOD) % MOD;
  
  long long ret = 0;
  REP (i, n) {
    long long pat = comb[i] * comb[n-1-i] % MOD;
    ret += pat * a[i] % MOD;
    ret %= MOD;
  }

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