You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[(4S)-4-(4-acetylpiperazin-1-yl)-1-oxa-9-azaspiro[5.5]undecan-9-yl]-2-phenoxyethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C23H33N3O4
assistant