You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-methylidene-3a-[[4-(pyrrolidine-1-carbonyl)phenyl]methyl]-1,4,6,6a-tetrahydrocyclopenta[c]furan-3-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H23NO3
assistant