import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N, M = getlist()
	D = []
	for i in range(M):
		d = int(input())
		D.append(d)

	D.sort()
	ans = INF
	# print(D)
	for i in range(M - N + 1):
		x = D[i]; y = D[i + N - 1]
		if y <= 0:
			ans = min(ans, abs(x))
		elif x >= 0:
			ans = min(ans, y)
		else:
			ans = min(ans, y - x + min(abs(x), abs(y)))

	print(ans)

if __name__ == '__main__':
	main()