import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

def f(x):
    ok = 0
    ng = 10 ** 18
    while ng - ok > 1:
        mid = ok + ng >> 1
        if mid * (mid + 1) // 2 <= x:
            ok = mid
        else:
            ng = mid
    return ok

def naive(x, n):
    for i in range(n):
        if x <= 0:
            x += i + 1
        else:
            x -= i + 1
        print(x)
    return x

x, n = na()
# print(naive(x, n))
k = min(n, f(abs(x)))

if x <= 0:
    x += k * (k + 1) // 2
else:
    x -= k * (k + 1) // 2
if n <= k:
    print(x)
    exit()

# print(n, k, x)
if (n - k) % 2 == 1:
    if x <= 0:
        x += k + 1
    else:
        x -= k + 1

# print(n, k, x)

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

print(x + f * ((n - k) // 2))