You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2'S,3R)-1'-[(R)-tert-butylsulfinyl]-6-methoxy-2'-(2-methylpropyl)spiro[1H-indole-3,3'-2H-pyrrole]-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H28N2O3S
assistant