You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
7-[(4-chlorophenyl)methyl]-8-[(2-chlorophenyl)methylamino]-1,3-dimethylpurine-2,6-dione is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H19Cl2N5O2
assistant