What equation would you to calculate the ideal mechanical advantage of a wheel and axle if the input force is on the axle?

The formula to calculate the ideal mechanical advantage (IMA) of a wheel and axle when the input force is applied to the axle is:

IMA = Radius of wheel (Rw) / Radius of axle (Ra)

Where Rw is the radius of the wheel and Ra is the radius of the axle.