n, m = map(int, raw_input().split())
l = sorted([int(raw_input()) for _ in range(m)])
ans = 100000
for i in range(len(l)-n+1):
	a = l[i]
	b = l[i+n-1]
	if a*b < 0:
		s = max(map(abs,[a,b])) + min(map(abs,[a,b])) * 2
	else:
		s = max(map(abs,[a,b]))
	ans = min(s,ans)
print ans