You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S,7aR)-N-(4-chloro-2-methylphenyl)-5-oxo-7a-phenyl-2,3,6,7-tetrahydropyrrolo[2,1-b][1,3]thiazole-3-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H19ClN2O2S
assistant