import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int M = scan.nextInt();
		int []D = new int[M];
		for(int i = 0; i < M; i++) {
			D[i] = scan.nextInt();
		}
		scan.close();
		int min = Integer.MAX_VALUE;
		for(int i = 0; i <= M - N; i++) {
			int l = D[i];
			int r = D[i + N - 1];
			if(r < 0 && l < 0) {
				min = Math.min(min, -l);
			}else if(l <= 0 && r >= 0) {
				int t = Math.min(2 * r - l, -2 * l + r);
				min = Math.min(min, t);
			}else {
				min = Math.min(min, r);
			}
		}
		System.out.println(min);
	}
}