You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by 2-[[4-(3,4-dimethoxyphenyl)sulfonylpiperazin-1-yl]methyl]-2-azaspiro[4.4]nonane-1,3-dione ?
user
C21H29N3O6S
assistant