You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 1'-(3-phenylpropyl)spiro[2,4,6,7,8,8a-hexahydro-1H-pyrrolo[1,2-a]pyrazine-3,4'-piperidine] .
user
C20H31N3
assistant