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

X=abs(x)

NG=10**18
OK=0

while NG>OK+1:
    mid=(OK+NG)//2

    if mid*(mid+1)//2<=X:
        OK=mid
    else:
        NG=mid

if n<=OK:
    p=n*(n+1)//2

    if x>0:
        print(x-p)
    else:
        print(x+p)
    exit()

p=OK*(OK+1)//2

if x>0:
    x-=p
else:
    x+=p

if (n-OK)%2==0:
    if x>0:
        x+=(n-OK)//2
    else:
        x-=(n-OK)//2

    print(x)
else:
    if x>0:
        x+=(n-OK)//2
        x-=n
    else:
        x-=(n-OK)//2
        x+=n

    print(x)