When a takes what value, the equation x3-3x2-a = 0 has exactly one real root, two unequal real roots and three unequal real roots?

When a takes what value, the equation x3-3x2-a = 0 has exactly one real root, two unequal real roots and three unequal real roots?

f(x)=x^3-3x^2-a
f'(x)=3x^2-6x=3x(x-2)=0---> x=0, 2
F (0) = - A is the maximum
F (2) = - 4-A is the minimum
When f (0) > 0, f (2) 0, - 4-A