x,n=map(int,input().split())
mode=0
if x<=0:
	mode=1
	x=-x

if x==0:
	lb=0
else:
	ub=n+1
	lb=0
	while ub-lb>1:
		t=(ub+lb)//2
		if x-t*(t+1)//2>0:
			lb=t
		else:
			ub=t

x=x-lb*(lb+1)//2
left=n-lb
if left%2==0:
	x+=left//2
else:
	x+=left//2
	x-=n

if mode:
	x=-x

print(x)