using System;
using System.Linq;
using System.Collections.Generic;
class Solution
{
    static void Main(string[] args)
    {
        var input = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int N = input[0];
        int K = input[1];
        var A = Console.ReadLine().Split().Select(long.Parse).ToArray();

        var nCk = new ModInt[N];//nCk[i]=K-1+i_C_K
        nCk[0] = 1;
        for (var i = 1; i < N; i++) nCk[i] = nCk[i - 1] * (K + i) / i;
        ModInt ans = 0;
        for (var i = 0; i < N; i++) ans += nCk[i] * nCk[N - 1 - i] * A[i];
        Console.WriteLine(ans.value);
    }
}
struct ModInt
{
    public long value;
    private const int MOD = 1000000007;
    //private const int MOD = 998244353;
    public ModInt(long value) { this.value = value; }
    public static implicit operator ModInt(long a)
    {
        var ret = a % MOD;
        return new ModInt(ret < 0 ? (ret + MOD) : ret);
    }
    public static ModInt operator +(ModInt a, ModInt b) => (a.value + b.value);
    public static ModInt operator -(ModInt a, ModInt b) => (a.value - b.value);
    public static ModInt operator *(ModInt a, ModInt b) => (a.value * b.value);
    public static ModInt operator /(ModInt a, ModInt b) => a * Modpow(b, MOD - 2);
    public static ModInt operator <<(ModInt a, int n) => (a.value << n);
    public static ModInt operator >>(ModInt a, int n) => (a.value >> n);
    public static ModInt operator ++(ModInt a) => a.value + 1;
    public static ModInt operator --(ModInt a) => a.value - 1;
    public static ModInt Modpow(ModInt a, long n)
    {
        var k = a;
        ModInt ret = 1;
        while (n > 0)
        {
            if ((n & 1) != 0) ret *= k;
            k *= k;
            n >>= 1;
        }
        return ret;
    }
    private static readonly List<long> Factorials = new List<long>() { 1 };
    public static ModInt Fac(long n)
    {
        for (var i = Factorials.Count(); i <= n; i++)
        {
            Factorials.Add((Factorials[i - 1] * i) % MOD);
        }
        return Factorials[(int)n];
    }
    public static ModInt nCr(long n, long r)
    {
        return n < r ? 0 : Fac(n) / (Fac(r) * Fac(n - r));
    }
    public static explicit operator int(ModInt a) => (int)a.value;
}