Consider a 20 kg uniform circular disc of radius 0.2 m. It is pin supported at its center and is at rest initially. The disk is acted upon by a constant force F=20 N through a massless string wrapped around its periphery as shown in the figure. 

Suppose the disc makes n number of revolutions to attain an angular speed of $50 rad s^{-1}$.
The value of n, to the nearest integer, is…………….
[Given : In one complete revolution, the disk rotates by 6.28 rad]