from itertools import *
from bisect import *
from collections import *
from heapq import *
import sys

sys.setrecursionlimit(10 ** 6)

def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def SI(): return sys.stdin.readline()[:-1]
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
int1 = lambda x: int(x) - 1
def MI1(): return map(int1, sys.stdin.readline().split())
def LI1(): return list(map(int1, sys.stdin.readline().split()))
p2D = lambda x: print(*x, sep="\n")
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

def main():
    n,m=MI()
    xx=[II() for _ in range(m)]
    xx.sort()
    ans=10**9
    for l in range(m-n+1):
        r=l+n-1
        if xx[r]<=0:ans=min(ans,-xx[l])
        elif xx[l]>=0:ans=min(ans,xx[r])
        else:ans=min(ans,min(-xx[l],xx[r])-xx[l]+xx[r])
    print(ans)

main()