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 $\bmod (10^9+7)$.

-----Sample Input-----
4 2
1 1 3 4

-----Sample Output-----
11

There are six ways to choose S: {1,1},{1,3},{1,4},{1,3},{1,4}, {3,4} (we distinguish the two 1s). The value of f(S) for these choices are 0,2,3,2,3,1, respectively, for the total of 11.

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