Angular acceleration

A nearly massless rod $(XY)$ of length $L$ is pivoted at one end $X$ so that it can swing free as a pendulum. Three masses $A(m),$ $B(2m)$ and $C(3m)$ are attached to it at the distances $\frac{L}{4},$ $\frac{L}{3}$ and $\frac{L}{2},$ respectively, from end $X.$ The rod is held horizontal and then it is released. Find the angular acceleration of the rod at the instant it is released.

The gravitational acceleration is $g.$