Grundy Values on a Game DAG

A token sits on a vertex of a directed acyclic graph; a move slides it along one outgoing edge, and a player who cannot move (token on a sink) loses. The edges are: S to A, S to B, S to C; A to two distinct sinks; B to A and B to a sink; C to B. Sinks have Grundy value 0. Compute the Grundy values of A, B, C, and S.