#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
#define CLR(t,v) memset(t,(v),sizeof(t))
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>void chmax(T&a,const T&b){if(a<b)a=b;}

ll nextLong() { ll x; scanf("%lld", &x); return x;}

const ll MOD = 1e9 + 7;

struct mint {
  ll x;
  mint(ll x=0):x((x%MOD+MOD)%MOD){}
  mint& operator+=(const mint a) {if ((x += a.x) >= MOD) x -= MOD;return *this;}
  mint& operator-=(const mint a) {if ((x += MOD-a.x) >= MOD) x -= MOD;return *this;}
  mint& operator*=(const mint a) {(x *= a.x) %= MOD;return *this;}
  mint operator+(const mint a) const {mint res(*this);return res+=a;}
  mint operator-(const mint a) const {mint res(*this);return res-=a;}
  mint operator*(const mint a) const {mint res(*this);return res*=a;}
  mint pow(ll b) const {
    mint res(1), a(*this);
    while (b) {
      if (b & 1) res *= a;
      a *= a;
      b >>= 1;
    }
    return res;
  }
  // for prime MOD
  mint inv() const {return pow(MOD-2);}
  mint& operator/=(const mint a) {return (*this) *= a.inv();}
  mint operator/(const mint a) const {mint res(*this);return res/=a;}
};
ostream& operator<<(ostream& os, const mint& a) {os << a.x; return os;}


const int SZ = 112345678;
ll inv[SZ];
ll fact[SZ];
ll fact_inv[SZ];
ll choose(int n, int r) {
  if (n < 0 || r < 0 || n < r) return 0;
  return fact[n] * fact_inv[n-r] % MOD * fact_inv[r] % MOD;
}

int main2() {
  int N = nextLong();
  int K = nextLong();
  vector<int> A(N);
  REP(i, N) A[i] = nextLong();

  mint ans = 0;
  REP(i, N) {
    mint val = mint(A[i]) * mint(choose(i+K, K)) * mint(choose(N-1-i+K, K));
    ans += val;
  }

  cout << ans << endl;
  return 0;
}

int main() {
  inv[1] = 1;
  for (int i = 2; i < SZ; i++) inv[i] = inv[(int) (MOD % i)] * (MOD - MOD / i) % MOD;
  fact[0] = 1;
  for (int i = 1; i < SZ; i++) fact[i] = fact[i-1] * i % MOD;
  fact_inv[0] = 1;
  for (int i = 1; i < SZ; i++) fact_inv[i] = fact_inv[i-1] * inv[i] % MOD;

#ifdef LOCAL
  for (;!cin.eof();cin>>ws)
#endif
    main2();
  return 0;
}