You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
benzyl 7-(4-methylphenyl)-6,8-dioxo-1,2,7-triazaspiro[4.4]non-2-ene-3-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H19N3O4
assistant