Third, ring tokens can be higher than 9 in which case the SMILES syntax represents the number prepended with the "%" character (e.g., "%10"). These rules apply to all SMILES variants used in this research. Lastly, the begin token "^" was prepended and the end token "$" appended to all SMILES strings. The tokenization process was performed independently for each database and yielded vocabulary sizes of 26 in GDB-13 and 31 in ChEMBL. When training the DeepSMILES models, the official implementation was used to convert the SMILES.