x, n = map(int, input().split())
import math

sqx = math.isqrt(abs(x) * 2)
sqx -= 1
while (sqx * (sqx + 1)) // 2 <= abs(x) :
	sqx += 1
sqx -= 1
if sqx >= n :
	s = n * (n + 1)
	s //= 2
	print(x - s if x > 0 else x + s)
else :
	s = (sqx * (sqx + 1)) // 2
	x = (x - s if x > 0 else x + s)
	m = n - sqx
	x += (m // 2) * (1 if x > 0 else -1)
	if m & 1 :
		x += n * (-1 if x > 0 else 1)
	print(x)