Apart from building blocks, the reaction pathway may also terminate at a dead-end molecule, which means no other reaction link with the molecule, or a maximum-depth molecule, which means the end point molecule reaches maximum allowed route depth from the target molecule, which was set to be 10 synthesis steps. The 'decision maker' fails to find a proper pathway in these cases, and therefore, adapted from Schreck et al., the penalty for a dead-end molecule is 100, and the penalty for a maximum-depth molecule is 10.