Problem Statement

We will play a one-player game using a number line and N pieces.

First, we place each of these pieces at some integer coordinate.

Here, multiple pieces can be placed at the same coordinate.

Our objective is to visit all of the M coordinates X_1, X_2, ..., X_M with these pieces, by repeating the following move:

Move: Choose a piece and let x be its coordinate. Put that piece at coordinate x+1 or x-1.

Note that the coordinates where we initially place the pieces are already regarded as visited.

Find the minimum number of moves required to achieve the objective.

Constraints

• All values in input are integers.
• 1 \leq N \leq 10^5
• 1 \leq M \leq 10^5
• -10^5 \leq X_i \leq 10^5
• X_1, X_2, ..., X_M are all different.

Sample Input 1

2 5
10 12 1 2 14

Sample Output 1

5

The objective can be achieved in five moves as follows, and this is the minimum number of moves required.

• Initially, put the two pieces at coordinates 1 and 10.
• Move the piece at coordinate 1 to 2.
• Move the piece at coordinate 10 to 11.
• Move the piece at coordinate 11 to 12.
• Move the piece at coordinate 12 to 13.
• Move the piece at coordinate 13 to 14.

Sample Input 2

3 7
-10 -3 0 9 -100 2 17

Sample Output 2

19

Sample Input 3

100 1
-100000

Sample Output 3

0