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

if x >= 0:
    ok = 1<<31
    ng = -1
    while ok - ng > 1:
        mid = (ok + ng) // 2
        if 2 * x <= mid * (mid + 1):
            ok = mid
        else:
            ng = mid
    k = ok
    if n < k:
        print(x - n * (n + 1) // 2)
    else:
        t = x - k * (k + 1) // 2
        if (n - k) % 2 == 0:
            print(t + (k - n) // 2)
        else:
            print(t + (n + k + 1) // 2)
else:
    ok = 1<<31
    ng = -1
    while ok - ng > 1:
        mid = (ok + ng) // 2
        if -2 * x < mid * (mid + 1):
            ok = mid
        else:
            ng = mid
    k = ok
    if n < k:
        print(x + n * (n + 1) // 2)
    else:
        t = x + k * (k + 1) // 2
        if (n - k) % 2 == 0:
            print(t + (n - k) // 2)
        else:
            print(t - (k + 1) - (n - k - 1) // 2)