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

if x < 0:
    f = 1
    x *= -1
else:
    f = 0

def is_ok(arg):
    S = arg * (arg + 1) // 2
    return S <= abs(x)

def bs(ok, ng):
    while abs(ok - ng) > 1:
        mid = (ok + ng) // 2
        if is_ok(mid):
            ok = mid
        else:
            ng = mid
    return ok

m = bs(0, 10**9 * 2)

if n <= m:
    S = n * (n+1) // 2
    x += (-1) * S
    x *= (-1) ** f
    print(x)
    exit()

S = m * (m+1) // 2
x += (-1) * S
x *= (-1) ** f
n -= m

if x <= 0:
    if n % 2 == 0:
        x -= n // 2
    else:
        x += m - (-n//2)
else:
    if n % 2 == 0:
        x += n // 2
    else:
        x -= m - (-n//2)

print(x)