import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int m = sc.nextInt();
        int n = sc.nextInt();
        int[] positions = new int[n];
        for (int i = 0; i < n; i++) {
            positions[i] = sc.nextInt();
        }
        Arrays.sort(positions);
        int ans = Integer.MAX_VALUE;
        for (int i = 0; i + m - 1 < n; i++) {
            int tmp = positions[i + m - 1] - positions[i] + Math.min(Math.abs(positions[i]),Math.abs(positions[i + m - 1]));
            ans = Math.min(ans, tmp);
        }
        System.out.println(ans);
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}