If OA, OC is the radius of ⊙ o, and OA ⊥ OC, point D is on arc AC, Ao = 1, arc ad = 2, arc CD, and point P is a moving point on OC, then the minimum value of AP + PD is

If OA, OC is the radius of ⊙ o, and OA ⊥ OC, point D is on arc AC, Ao = 1, arc ad = 2, arc CD, and point P is a moving point on OC, then the minimum value of AP + PD is

The answer is: 3 under the root