Rollout is performed using the same GCN model used in the Expansion step to evaluate the added child nodes. Unlike the fragment-wise search, the fragments are generated from scratch; therefore, the terminal state can be defined in the same way as for existing methods. A state is treated as a terminal if the GCN model predicts an empty atom or when no bonds are predicted. The generated fragments are added to the molecule selected in the Selection step of MCTS in the fragment-wise search to obtain a new molecule, and the value of the evaluation function for that molecule is used as the reward.