You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-2-[(4S,4aS,5S,6S,8aR)-2-amino-5-hydroxy-4,8a-dimethyl-4a,5,6,7,8,9-hexahydro-4H-benzo[f][1,3]benzothiazol-6-yl]-1-thiomorpholin-4-ylpropan-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H31N3O2S2
assistant