n,m,*d=gets(p).split.map(&:to_i)
d.sort!
puts (m-n+1).times.map{|i|
	if d[i]<=0&&0<=d[i+n-1]
		d[i].abs+d[i+n-1].abs+[d[i].abs,d[i+n-1].abs].min
	else
		[d[i].abs,d[i+n-1].abs].max
	end
}.min