For a finite set of integers X, let f(X)=\max X - \min X.

Given are N integers A_1,...,A_N.

We will choose K of them and let S be the set of the integers chosen. If we distinguish elements with different indices even when their values are the same, there are {}_N C_K ways to make this choice. Find the sum of f(S) over all those ways.

Since the answer can be enormous, print it \bmod (10^9+7).

Constraints

* 1 \leq N \leq 10^5
* 1 \leq K \leq N
* |A_i| \leq 10^9

Input

Input is given from Standard Input in the following format:


N K
A_1 ... A_N


Output

Print the answer \bmod (10^9+7).

Examples

Input

4 2
1 1 3 4


Output

11


Input

6 3
10 10 10 -10 -10 -10


Output

360


Input

3 1
1 1 1


Output

0


Input

10 6
1000000000 1000000000 1000000000 1000000000 1000000000 0 0 0 0 0


Output

999998537

import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;

import java.util.*;

public class Main {
    long MOD = (long) 1e9 + 7;

    InputStream in;
    OutputStream out;

    public Main() {
        this(System.in, System.out);
    }

    public Main(InputStream in, OutputStream out) {
        this.in = in;
        this.out = out;
    }

    void run() {
        Scanner sc = new Scanner(this.in);
        PrintWriter out = new PrintWriter(this.out);

        // write your code
        int n = sc.nextInt(), k = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        Arrays.sort(a);

        long ans = 0;
        Combination comb = new Combination(n, MOD);

        for (int i = 0; i < n; i++) {
            ans = (ans + 1L * (MOD + a[n - i - 1]) % MOD * comb.nck(n - i - 1, k - 1) % MOD) % MOD;
            ans = (ans - 1L * (MOD + a[i]) % MOD * comb.nck(n - i - 1, k - 1) % MOD + MOD) % MOD;
        }

        out.println(ans);

        out.flush();
    }

    public class Combination {
        int n;
        long mod;
        long[] facts;

        public Combination(int n, long mod) {
            this.n = n;
            this.mod = mod;
            facts = new long[n];
            facts[0] = 1;
            for (int i = 1; i < n; i++) {
                facts[i] = facts[i - 1] * i % mod;
            }
        }

        long modpow(long a, long b) {
            if (b == 0) return 1;
            else if (b == 1) return a;

            long x = modpow(a, b / 2);
            return b % 2 == 0 ? x * x % mod : x * (x * a % mod) % mod;
        }

        long inv(long n) {
            return modpow(n, mod - 2);
        }

        public long nck(int n, int k) {
            return n < k ? 0 : facts[n] * (inv(facts[n - k]) * inv(facts[k]) % mod) % mod;
        }
    }


    void debug(Object... os) {
        System.err.println(Arrays.deepToString(os));
    }

    public static void main(String[] args) {
        new Main().run();
    }
}