x,n = map(int,input().split())
rev = 0

if x < 0: 
    rev = 1
    x *= -1
    

l,r = 0,n
while r - l > 1:

    mid = (r + l) // 2
    if mid * (mid + 1) // 2 >= x:
        r = mid
    else:
        l = mid
        

s = x - (r * (r + 1) // 2)

if (n - r) % 2 == 0:

    ans = s - ((n - r) // 2)
    if rev == 1:
        print(-ans)
    else:
        print(ans)

else:

    rr = r + 1
    ans = (s + rr) + ((n - rr) // 2)

    if rev == 1:
        print(-ans)
    else:
        print(ans)