A small ball is suspended by a thread of length l = 1 m at the point O on the wall, forming a small angle α=2∘ with the vertical (as shown in figure). Then the thread with ball was deviated through a small angle β=4∘ and set free. Assuming the collision of the ball against the wall to be perfectly elastic, the oscillation period of such a pendulum (in seconds) is ___________ (Take g=π2).