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.

Input

Input is given from Standard Input in the following format:

N M
X_1 X_2 ... X_M

Output

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