Problem:
Score : 300 points

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.

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

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

class Main{


	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] x = new int[m];

		for(int i = 0;i < m;i++){
			x[i] = sc.nextInt();
		}
		Arrays.sort(x);

		ArrayList<Pair> pairs = new ArrayList<Pair>();
		int[] dis = new int[m];
		for(int i = 0;i < m-1;i++){
			dis[i] = x[i+1]-x[i];
		}
		Arrays.sort(dis);
		long ans = 0;
			for(int i = 0;i <=m-n;i++){

				ans += dis[i];
			}
		
	

		System.out.println(ans);

	}


	static int lowerbond(long k, long[] data){		//kより小さい最小の値をdataの中から探し、返す二分探索
		int min = 0;
		int max = data.length-1;

		while(max-min >= 0){
			int mid = (max+min)/2;
			if(data[mid] >= k){
				max = mid-1;
			}else{
				min = mid+1;
			}
		}
		return min;
	}









	class UnionFind{
		int[] parent;
		public UnionFind(int N){
			this.parent = new int[N];
			for(int i = 0; i < N;i++){
				parent[i] = i;
			}
		}
		public int root(int x){			//根要素を取得
			if(parent[x] == x){			//初期状態
				return x;
			}else{
				return parent[x] = root(parent[x]);    	//再帰によって根を取得
			}
		}
		public void unite(int x,int y){ 	//統合メソッド
			if(same(x,y)){					//同じ根なら終了
				return;
			}
			int xroot = root(x);
			int yroot = root(y);
			parent[xroot] = yroot;			//統合
			return;

		}

		public boolean same(int x,int y){			//根が同じか（同じグループに属しているか）を判定
			return(root(x) == root(y));
		}
	}

}

class Pair implements Comparable{
	int from;		//p
	int end;		//y
	int num;
	int bango;
	@Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return from - otherpair.from;
	}
}