What's the period of this physical pendulum?

Question

A small thin disk of radius r and mass m is attached rigidly to the face of a second thin disk of radius R and mass M as shown below. The center of the small disk is located at the edge of the large disk. The large disk is mounted at its center on a frictionless axle. The assembly is rotated through a small angle and released. Find the period of the motion.

Answer 1

This is a simple pendulum with a period T
T=2 pi sqrt(L/g)
pi = 3.14159..
g- acceleration due to gravity
L - distance from the center of gravity to the pivot point.

So finally
T=2 pi sqrt(R/g)