use std::cmp::{max, min};

fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<usize> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nm[0];
    let m = nm[1];
    let mut d: Vec<isize> = vec![];
    for _ in 0..m {
        let mut dtemp = String::new();
        std::io::stdin().read_line(&mut dtemp).ok();
        let dtemp: isize = dtemp.trim().parse().unwrap();
        d.push(dtemp);
    }
    d.sort();

    let mut result: usize = 1000000000;
    for i in 0..m-n+1 {
        let left = d[i];
        let right = d[i+n-1];
        let maxval = max(left.abs() as usize, right.abs() as usize);
        let minval = min(left.abs() as usize, right.abs() as usize);
        if left * right < 0 {
            result = min(result, maxval + 2 * minval);
        } else {
            result = min(result, maxval);
        }
    }
    println!("{}", result);
}