import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] arr = new int[m];
		for (int i = 0; i < m; i++) {
		    arr[i] = sc.nextInt();
		}
		Arrays.sort(arr);
		int minStart;
		if (arr[0] >= 0) {
		    minStart = 0;
		} else if (arr[m - 1] < 0) {
		    minStart = m;
		} else {
    		int left = 0; 
    		int right = arr.length - 1;
    		while (right - left > 1) {
    		    int mm = (left + right) / 2;
    		    if (arr[mm] >= 0) {
    		        right = mm;
    		    } else {
    		        left = mm;
    		    }
    		}
    		minStart = right;
		}
		int min = Integer.MAX_VALUE;
		for (int i = 0; i <= n; i++) {
		    if (minStart - i < 0 || minStart + n - i - 1 > m - 1) {
		        continue;
		    }
		    if (i == 0) {
		        min = Math.min(min, arr[minStart + n - i - 1]);
		    } else if (i == n) {
		        min = Math.min(min, - arr[minStart - i]);
		    } else {
    		    min = Math.min(min, - arr[minStart - i] * 2 + arr[minStart + n - i - 1]);
    		    min = Math.min(min, - arr[minStart - i] + arr[minStart + n - i - 1] * 2);
		    }
		}
	    System.out.println(min);
	}
}