You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Under IUPAC nomenclature, a molecule named 5'-phenylspiro[1,3-dioxolane-2,3'-4,4a,5,8-tetrahydro-2H-benzo[7]annulene]-9',9'-dicarbonitrile is given. What is its corresponding molecular formula?
user
C21H20N2O2
assistant