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

public class Main {

    static void solve() {
        int n = nextInt();
        int k = nextInt();
        List<Integer> a = nextIntList(n);

        sort(a);

//        c = new long[n + 1][k + 1];
        comWithModInit(n);

        long ans = 0;
        for (int i = 0; i < n - 1; i++) {
//            System.out.println((n - 1 - i) + ":" + (k - 1));
//            ans += (a.get(n - 1 - i) - a.get(i)) * c(n - 1 - i, k - 1);
//            ans += (a.get(n - 1 - i) - a.get(i)) * comWithMod(n - 1 - i, k - 1);
            ans += (a.get(n - 1 - i) - a.get(i)) * comWithMod(n - 1 - i, k - 1) % MOD;
        }
        ans %= MOD;
        out.println(ans);
    }

    static final int MOD = 1_000_000_007;
    static long[] fac, finv, inv;

    // nCkの初期化
    static void comWithModInit(int max) {
        fac = new long[max];
        finv = new long[max];
        inv = new long[max];
        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;
        }
    }

    // nCkの計算
    static long comWithMod(int n, int k) {
        if (n < k)
            return 0;
        if (n < 0 || k < 0)
            return 0;
        return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
    }

    static long[][] c;

    // nCk
    // nCk = n-1Ck + n-1Ck-1
    static long c(int n, int k) {
        if (c[n][k] != 0)
            return c[n][k];

        if (n == k) {
            return 1;
        }
//        if (n >= 1) {
        if (k >= 1) {
            return c[n][k] = c(n - 1, k) + c(n - 1, k - 1);
        } else {
            return 1;
        }
//        }

//        return kaijo(n) / kaijo(n - k) / kaijo(k);
    }

//    // nCk
//    // nCk = n-1Ck + n-1Ck-1
//    static long c(long n, long k) {
//        if (n == k) {
//            return 1;
//        }
//        if (n >= 1) {
//            if (k >= 1) {
//                return c(n - 1, k) + c(n - 1, k - 1);
//            } else {
//                return 1;
//            }
//        }
//
//        return kaijo(n) / kaijo(n - k) / kaijo(k);
//    }
//
//    static long kaijo(long a) {
//        if (a <= 1)
//            return 1;
//        return a * kaijo(a - 1);
////        return a * kaijo(a - 1) % MOD;
//    }

    static PrintWriter out;
    static Scanner sc;

    static int[][] newIntArray(int h, int w, int value) {
        int[][] ret = new int[h][w];
        for (int i = 0; i < h; i++) {
            for (int j = 0; j < w; j++) {
                ret[i][j] = value;
            }
        }
        return ret;
    }

    static int nextInt() {
        return Integer.parseInt(sc.next());
    }

    static long nextLong() {
        return Long.parseLong(sc.next());
    }

    static String nextString() {
        return sc.next();
    }

    static int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextInt();
        }
        return a;
    }

    static List<Integer> nextIntList(int n) {
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(nextInt());
        }
        return list;
    }

    static List<Double> nextDoubleList(int n) {
        List<Double> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add((double) nextInt());
        }
        return list;
    }

    static List<Long> nextLongList(int n) {
        List<Long> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(nextLong());
        }
        return list;
    }

    static char[][] nextCharArray(int h, int w) {
        char[][] c = new char[h][w];
        for (int i = 0; i < h; i++) {
            String str = nextString();
            for (int j = 0; j < w; j++) {
                c[i][j] = str.charAt(j);
            }
        }
        return c;
    }

    static <T extends Comparable<? super T>> void sort(List<T> list) {
        Collections.sort(list);
    }

    // greatest common divisor
    // 最大公約数
    static long gcd(long a, long b) {
        if (b == 0) {
            return a;
        }
        return gcd(b, a % b);
    }

    // least common multiple
    // 最小公倍数
    static long lcm(long a, long b) {
        return a * b / gcd(a, b);
    }

    // baseのn乗を計算を返す
    static int pow(int base, int n) {
        int ret = 1;
        for (int i = 0; i < n; i++) {
            ret *= base;
        }
        return ret;
    }

    // return n^k mod m
    static long powMod(long n, long k, long m) {
        if (k == 0) {
            return 1;
        } else if (k % 2 == 1) {
            return powMod(n, k - 1, m) * n % m;
        } else {
            long tmp = powMod(n, k / 2, m);
            return tmp * tmp % m;
        }
    }

    // intをlength桁のbit文字列に変換
    static String toBitString(int length, int n) {
        StringBuilder sb = new StringBuilder();
        for (int i = length - 1; i >= 0; i--) {
            if ((n >> i) % 2 == 1) {
                sb.append("1");
            } else {
                sb.append("0");
            }
        }
        return sb.toString();
    }

//    // intをlength桁のbit文字列に変換
//    static String toBinaryString(int input, int length) {
//        return toBinaryString(input).substring(29 - length);
//    }
//
//    // intを29桁のbit文字列に変換
//    static String toBinaryString(int input) {
//        String ret = "";
//        int max = 0x10000000;
//        for (int i = 0; i < 29; i++) {
//            int tmp = input / max;
//            ret += tmp;
//            input %= max;
//            max /= 2;
//        }
//        return ret;
//    }

    public static void main(String[] args) {
        out = new PrintWriter(System.out);
        sc = new Scanner(System.in);

        solve();

        out.flush();
        sc.close();
    }

}
