import math
import sys
from typing import List, Tuple


def int1(x: str, /): return int(x) - 1


def input(): return sys.stdin.readline().rstrip('\n')


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    n, m = map(int, input().split())
    d = sorted(int(input()) for _ in range(m))
    ans = math.inf
    for i in range(m - n + 1):
        fi, la = d[i], d[i + n - 1]
        ds = max(abs(fi), abs(la)) if fi * la > 0 else abs(fi) + abs(la) + min(abs(la), abs(fi))
        ans = min(ans, ds)

    return ans

def _start():
    ret = main()

    if ret is not None:
        if isinstance(ret, List) or isinstance(ret, Tuple):
            print(*ret)
        else:
            print(ret)


if __name__ == '__main__':
    _start()