PL-OM 2017 Problem 1

Points $P$ and $Q$ lie respectively on sides $AB$ and $AC$ of a triangle $ABC$ and $BP=CQ$ . Segments $BQ$ and $CP$ cross at $R$ . Circumscribed circles of triangles $BPR$ and $CQR$ cross again at point $S$ different from $R$ . Prove that point $S$ lies on the bisector of angle $BAC$ .