You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-(3-chloro-4-isocyanophenyl)-5,5-dimethyl-1-(4-propan-2-yloxyphenyl)-2-sulfanylideneimidazolidin-4-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H20ClN3O2S
assistant