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

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

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

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

if n % 2:
    x *= -1

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

print(x)