You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(4-methyl-2-nitrophenyl)-4-(1,8,8-trimethyl-2,4-dioxo-3-azabicyclo[3.2.1]octan-3-yl)butanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H27N3O5
assistant