import java.util.Scanner;

public class Yuki370 {
	static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		int N, M;
		N = sc.nextInt();
		M = sc.nextInt();
		int[] D = new int[M];
		for (int i = 0; i < M; i++) {
			D[i] = sc.nextInt();
		}
		int ans = (int) 1e9;
		for (int i = 0; i + N - 1 < D.length; i++) {
			if (0 <= D[i]) {
				ans = Math.min(ans, Math.abs(D[i + N - 1]));
			} else if (D[i] < 0 && 0 < D[i + N - 1]) {
				int buf = Math.abs(D[i]) * 2 + Math.abs(D[i + N - 1]);
				buf = Math.min(buf, Math.abs(D[i]) + Math.abs(D[i + N - 1]) * 2);
				ans = Math.min(ans, buf);
			} else {
				ans = Math.min(ans, Math.abs(D[i]));
			}
		}
		System.out.println(ans);
	}
}