def SUM(l, r, c):
    return (l+r)*c//2

X, N = map(int, input().split())

left = 0
right = 10**10
while left+1 < right:
    mid = (left+right)//2
    if SUM(1, mid, mid) < abs(X):
        left = mid
    else:
        right = mid

if N <= right:
    if X <= 0:
        print(X+SUM(1, N, N))
    else:
        print(X-SUM(1, N, N))
    exit()

if X <= 0:
    X += SUM(1, right, right)
else:
    X -= SUM(1, right, right)

l, r = right+1, N
if X <= 0:
    if l%2 == r%2:
        X += SUM(l, r, (r-l)//2+1)
        if l < r:
            X -= SUM(l+1, r-1, (r-l)//2)
    else:
        X += SUM(l, r-1, (r-l)//2+1)
        X -= SUM(l+1, r, (r-l)//2+1)
else:
    if l%2 == r%2:
        X -= SUM(l, r, (r-l)//2+1)
        if l < r:
            X += SUM(l+1, r-1, (r-l)//2)
    else:
        X -= SUM(l, r-1, (r-l)//2+1)
        X += SUM(l+1, r, (r-l)//2+1)

print(X)