import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeMap;

public class Main {
	
	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		final int M = sc.nextInt();
		
		int[] pos = new int[M];
		for(int i = 0; i < M; i++){
			pos[i] = sc.nextInt();
		}
		
		int answer = Integer.MAX_VALUE;
		for(int fst = 0; fst <= M - N; fst++){
			final int snd = fst + N - 1;
			
			answer = Math.min(answer, (Integer.signum(pos[fst]) == Integer.signum(pos[snd])) ? 
					Math.max(Math.abs(pos[fst]), Math.abs(pos[snd])) : 
						(Math.min(Math.abs(2 * pos[fst]) + Math.abs(pos[snd]), Math.abs(pos[fst]) + 2 * Math.abs(pos[snd]))));
			
		}
	
		System.out.println(answer);
	}
	
	public static class Scanner implements Closeable {
		private BufferedReader br;
		private StringTokenizer tok;
 
		public Scanner(InputStream is) throws IOException {
			br = new BufferedReader(new InputStreamReader(is));
		}
 
		private void getLine() throws IOException {
			while (!hasNext()) {
				tok = new StringTokenizer(br.readLine());
			}
		}
 
		private boolean hasNext() {
			return tok != null && tok.hasMoreTokens();
		}
 
		public String next() throws IOException {
			getLine();
			return tok.nextToken();
		}
 
		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}
 
		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}
 
		public void close() throws IOException {
			br.close();
		}
	}
}