#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

const int MAX = 1000000;
long long fac[MAX], finv[MAX], inv[MAX];


void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

long long COM(ll n,ll k){
        if(n < k) return 0;
        if(n < 0 || k < 0) return 0;
        k = min(k,n-k);
        ll res = 1;
        for(int i=1;i <= k;i++){
                res = (res * (n-i+1))%MOD;
        }
        
        res = (res * finv[k]) %MOD;
        return res;
}

long long modpow(long long x, long long n) {
    long long ret = 1;
    while (n > 0) {
        if (n & 1) ret = (ret * x) % MOD;  
        x = (x * x) % MOD;
        n >>= 1;  
    }
    return ret;
}


/*繰り返し二乗法でxのmod逆元を取る*/
long long inverse(long long x){
    return modpow(x,MOD-2);
}

int main(){
    COMinit();
    int n,k;
    cin >> n >> k;
    vector<ll> a(n);
    rep(i,n) cin >> a[i];
    ll ans = 0;
    ll c1 = 1;
    ll c2 = COM(k+n-1,n-1);
    rep(i,n){
        ans += ((c1 * c2)%MOD * a[i])%MOD;
        ans %= MOD;
        c1 = (c1 * (k+i+1))%MOD;
        c1 = (c1 * inverse(i+1))%MOD;
        c2 = (c2 * (n-i-1))%MOD;
        if(k+n-i-1!=0)c2 = (c2 * inverse(k+n-i-1))%MOD;
    }
    cout << ans << endl;
    return 0;
}