You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6-(3-fluoropyridine-2-carbonyl)-N-(pyridin-3-ylmethyl)-6-azaspiro[3.4]octane-8-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21FN4O2
assistant