A uniform cylinder of length $L$ and mass $M$ having cross–sectional area $A$ is suspended, with its length vertical from a fixed point by a massless spring, such that it is half submerged in a liquid of density $\sigma$ at equilibrium position. When the cylinder is given a small downward push and released it starts oscillating vertically with small amplitude. If the force constant of the spring is $k$, calculate the frequency of oscillations of cylinder.