x, n = map(int, input().split())
i = 0
if x > 0:
    # x-i(i+1)/2<=0
    l, r = 0, 10 ** 10
    while r - l > 1:
        c = (l + r) // 2
        if c * (c + 1) // 2 >= x:
            r = c
        else:
            l = c
    i = min(l, n)
    x -= i * (i + 1) // 2
else:
    # x+i(i+1)/2>0
    l, r = 0, 10 ** 10
    while r - l > 1:
        c = (l + r) // 2
        if x + c * (c + 1) // 2 > 0:
            r = c
        else:
            l = c
    i = min(r, n)
    x += i * (i + 1) // 2
t = (n - i) // 2
x += t
i += 2 * t
if i < n:
    x -= n
print(x)