You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-N-methyl-1-N-(3-methylbutyl)-3-N-phenylimidazo[1,5-a]pyridine-1,3-dicarboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24N4O2
assistant