TH-TMO 2006 Problem 1

Let $O$ be the circumcenter of a triangle $\vartriangle ABC$ . It is given that $\angle ABC = 70^o$ , $\angle ACB =50^o$ . Let the angle bisector of $\angle BAC$ intersect the circumcircle of $\vartriangle ABC$ again at $D$ . Compute $\angle ADO$ .