#include <bits/stdc++.h>
using namespace std;
//#include <atcoder/all>
//using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define MAX 200003
#define MOD 1000000007
#define INF 1000000000

ll modpow(ll a,ll x){
  ll ret=1;
  a%=MOD;
  while(x>0){
    if(x%2==1){
      ret=ret*a%MOD;
    }
    a=a*a%MOD;
    x>>=1;
  }
  return ret;
}

ll modinv(ll x){
  return modpow(x,MOD-2);
}


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

  /*
  if(K==0){
    ll ans=0;
    for(int i=0;i<N;i++){
      ans+=A[i];
    }
    cout<<ans<<endl;
    return 0;
  }
  */

  vector<ll> com(N+1,0);
  com[0]=1;
  for(int i=1;i<=N;i++){
    com[i]=com[i-1];
    com[i]=com[i]*(K+(ll)i)%MOD;
    com[i]=com[i]*modinv(i)%MOD;
  }
  ll ans=0;
  for(int i=0;i<N;i++){
    ll cnt=com[i]*com[N-i-1]%MOD;
    //ll cnt=COM(K+i,i)*COM(K+(N-i-1),(N-i-1))%MOD;
    ans+=A[i]*cnt;
    ans%=MOD;
  }
  cout<<ans<<endl;
}