You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[3-[(3aR,5R,7aS)-5-methyl-1,3-dioxo-3a,4,5,6,7,7a-hexahydroisoindol-2-yl]phenyl] benzenesulfonate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21NO5S
assistant