#!/usr/bin/env python3


def calc_distance(selected_gabbages):
    left = abs(min(selected_gabbages[0], 0))
    right = max(selected_gabbages[-1], 0)
    dist_l = left * 2 + right
    dist_r = right * 2 + left
    return min(dist_l, dist_r)


def compute_minimum_distance(n, m, ds):
    return min(calc_distance(ds[i: i + n]) for i in range(m - n + 1))


def main():
    n, m = map(int, input().split())
    ds = sorted(int(input()) for _ in range(m))
    print(compute_minimum_distance(n, m, ds))


if __name__ == '__main__':
    main()