/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.07.03 22:05:50
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int MOD = 1e9 + 7;
struct mint {
private:
    long long x;
public:
    mint(long long x = 0) :x((MOD+x)%MOD) {}
    mint(std::string &s) {
        long long z = 0;
        for (int i = 0; i < s.size(); i++) {
            z *= 10;
            z += s[i] - '0';
            z %= MOD;
        }
        this->x = z;
    }
    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) {
        long long n = MOD - 2;
        mint u = 1, b = a;
        while (n > 0) {
            if (n & 1) {
                u *= b;
            }
            b *= b;
            n >>= 1;
        }
        return *this *= u;
    }
    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 operator/(const mint &a) const {
        mint res(*this);
        return res /= a;
    }
    friend std::ostream& operator<<(std::ostream &os, const mint &n) {
        return os << n.x;
    }
    bool operator==(const mint &a) const {
        return this->x == a.x;
    }
};

long long powMod(long long k, long long n, long long mod) {
    long long x = 1;
    while (n > 0) {
        if (n & 1) {
            x = x * k % mod;
        }
        k = k * k % mod;
        n >>= 1;
    }
    return x;
}

long long comb(ll n, ll r, ll mod) {
    long long ret = 1;
    while (true) {
        if (r == 0) break;
        long long N = n % mod;
        long long R = r % mod;
        if (N < R) return 0;
        for (int i = 0; i < R; i++)
        {
            ret = ret * (N - i) % mod;
        }
        long long imul = 1;
        for (int i = 0; i < R; i++)
        {
            imul = imul * (i + 1) % mod;
        }
        ret = ret * powMod(imul, mod - 2, mod) % mod;
        n /= mod; r /= mod;
    }
    return ret;
}
int main() {
    int n, k;
    cin >> n >> k;
    mint ans = 0;
    for (int i = 0; i < n; i++) {
        int a;
        cin >> a;
        ans += mint(comb(n - i + k - 1, k, MOD)) * comb(k + i, i, MOD) * a;
    }
    cout << ans << endl;
    return 0;
}