π1 is a plane passing through the point (1, 2, 3) and perpendicular to the planes x + 2y + 3z - 6 = 0 , x + 2y + 2z - 5 = 0. If (- 1 , 2 , - 3) is the foot of the perpendicular drawn from the point (1 , 3 , 2) on to the plane π2 , then the angle between the planes π1 and π2 is