x, n = gets.split.map(&:to_i)

y = x.abs
ac = n
wa = -1
while ac - wa > 1
	wj = (ac + wa) >> 1
	sum = (1 .. wj).sum
	if sum >= y
		ac = wj
	else
		wa = wj
	end
end

ac = [ac - 1, 0].max
current = x <= 0 ? x + (1 .. ac).sum : x - (1 .. ac).sum

e = (n - ac) / 2
o = (n - ac) % 2
if current <= 0
	current -= e
	current += n if o == 1
else
	current += e
	current -= n if o == 1
end

puts current