You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5,6-dichloro-2-[[4-(4-methoxyphenyl)piperazin-1-yl]methyl]isoindole-1,3-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H19Cl2N3O3
assistant