x,n = map(int,input().split())
if x<=0:
  ng,ok = 0,n
  while ok-ng>1:
    i = ok+ng>>1
    if x+i*(i+1)//2>0:
      ok = i
    else:
      ng = i
  x += ok*(ok+1)//2
  t = ok+1
  sgn = -1
else:
  ng,ok = 0,n
  while ok-ng>1:
    i = ok+ng>>1
    if x-i*(i+1)//2<=0:
      ok = i
    else:
      ng = i
  x -= ok*(ok+1)//2
  t = ok+1
  sgn = 1
def f(t,n):
  if t>n:
    return 0
  m = (n-t)//2+1
  return (t+(t+2*(m-1)))*m//2
x += (f(t,n)-f(t+1,n))*sgn
print(x)