Two uniform ropes having linear mass densities m and 4m, length l. Each are joined to form a closed loop. The loop is hanging over a fixed frictionless small pulley with the lighter rope above as shown in the figure (in the figure equilibrium position is shown). Now if the point A joint, is slightly displaced in downward direction and released. It is found that, the loop perform angular SHM with the period of the oscillation equal to 2N. The value of N (take l=150π2 metre) is _________.