For a unit step input, the response of a second order system is y(t) = K (1 - e^{-t/τ} - (t/τ) e^{-t/τ}) where, K is the steady state gain, τ is the damping coefficient, ω is the natural period of oscillation and φ is the phase lag. The overshoot of the system is exp (-π ζ / √(1 - ζ^2)). For a unit step input, the response of the system from an initial steady state condition at t = 0 is shown in the figure below. What is the natural period of oscillation (in seconds) of the system?