N,M = map(int,raw_input().split())
dust = [int(raw_input()) for i in xrange(M)]
dust.sort()
ans = 30001
for i in xrange(M-N+1):
	ld = dust[i]
	rd = dust[i+N-1]
	if rd <= 0:
 		ans = min(ans,-ld)
	elif ld >= 0:
		ans = min(ans,rd)
	else:
		ans = min(ans,min(rd,-ld)*2+max(rd,-ld))
print ans