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

l = 0
r = n
while r - l > 1:
  m = (l + r) // 2
  if (m * (m + 1)) // 2 <= abs(x):
    l = m
  else:
    r = m
y = abs(x) - (l * (l + 1)) // 2 + (n - r + 1) // 2
if n >= r and (n - r) % 2 == 0:
  y -= n
if x <= 0:
  y = -y
print(y)