import math


def circleSDF(x, y, cx, cy, cr):
    """Return: 
    negative if (x, y) is inside the circle;
    positive if (x, y) is outside the circle;
    zero if (x, y) is on the circle
    """
    return math.sqrt((x - cx) * (x - cx) + (y - cy) * (y - cy)) - cr