3a

def get_area(S, C, D):

    def dist(a, b):
        return ((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2) ** (1/2)

    pink1 = (0, S/2 - D/2)
    pink2 = (S/2 - D/2, 0)
    pink3 = (0, -S/2 + D/2)
    pink4 = (-S/2 + D/2, 0)

    white, pink = 0, 0

    for i in range(100000):
        P = (random()*S - S/2, random()*S - S/2)


        if (dist(P, pink1) < D/2 or dist(P, pink2) < D/2 or dist(P, pink3) < D/2 or dist(P, pink4) < D/2) and dist(P, (0,0)) > C/2:
            pink += 1
        else:
            white += 1

    return S**2 * (pink / (white+pink))