In Control Engineering, servomotors with tachometer feedback can be modeled by the second order system

 K / [J*s^2 + (B + K*K_v)*s + K] 

Depending on the damping ratio of the servomotor, the system can be classified as underdamped, critically damped or overdamped. In this problem, you will be given the following as input:

B - damping of servomotor (viscous and friction elements)

J - inertia of servomotor

K - gain of proportional controller

K_v - velocity feedback constant of tachometer

You are to correctly classify the system by returning either ' underdamped ', ' critical ' or ' overdamped '.