You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-(4-chlorophenyl)-N-(2,4-dichlorophenyl)-5-methyl-2,4-dioxo-4a,7a-dihydro-1H-pyrrolo[3,2-d]pyrimidine-7-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H15Cl3N4O3
assistant