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.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static int MAX = 510000;
	public static int MOD = 1000000007;

	public static long[] f = new long[MAX];
	public static long[] finv = new long[MAX];
	public static long[] inv = new long[MAX];

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

	public static long Com(int n, int k) {
		if(n < k)
			return 0;
		if(n < 0 || k < 0)
			return 0;
		return f[n] * (finv[k] * finv[n - k] % MOD) % MOD;
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		List<Long> list = new ArrayList<>();
		for(int i = 0; i < n; i++) {
			list.add(sc.nextLong());
		}
		Collections.sort(list);
		ComInit();
		long ans = 0;
		if(k == 1) {
			System.out.println(0);
		} else {
			for(int i = 0; i < n; i++) {
				if(n - i - 1 >= k - 1) {
					ans -= list.get(i) * Com(n - i - 1, k - 1);
					ans %= MOD;
				}
				if(i >= k - 1) {
					ans += list.get(i) * Com(i, k - 1);
					ans %= MOD;
				}
			}
			System.out.println(ans);
		}

	}

}
