x, n = map(int, input().split()) y = abs(x) l = 0 r = 1 << 31 while r - l > 1: mid = (l + r) // 2 if mid * (mid + 1) // 2 > y: r = mid else: l = mid if mid > n: if x > 0: x -= n * (n + 1) // 2 else: x += n * (n + 1) // 2 print(x) exit() y -= l * (l + 1) // 2 zero = y == 0 pm = -1 for l_ in [r, r + 1]: r_ = n if r_ % 2 != l_ % 2: r_ -= 1 y += pm * (l_ + r_) * ((r_ - l_) // 2 + 1) // 2 pm *= -1 if zero: print(-y) elif x > 0: print(y) else: print(-y)