x,n=map(int,input().split())
if x>0:
  ok=0
  ng=10**10
  while ng-ok>1:
    m=(ok+ng)//2
    if x-m*(m+1)//2>0:
      ok=m
    else:
      ng=m
  if ok>=n:
    print(x-n*(n+1)//2)
    exit()
  x-=ok*(ok+1)//2
  if (n-ok)%2:
    print(x+(n-ok)//2-n)
  else:
    print(x+(n-ok)//2)
  exit()
if x==0:
  if n%2:
    print(-n//2+n)
  else:
    print(-n//2)
  exit()
if x<0:
  ok=0
  ng=10**10
  while ng-ok>1:
    m=(ok+ng)//2
    if x+m*(m+1)//2<0:
      ok=m
    else:
      ng=m
  if ok>=n:
    print(x+n*(n+1)//2)
    exit()
  x+=ok*(ok+1)//2
  if (n-ok)%2:
    print(x-(n-ok)//2+n)
  else:
    print(x-(n-ok)//2)
  exit()