You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(7R)-1,7-dimethyl-2,4-dioxo-9-phenyl-7,8-dihydro-6H-purino[7,8-a]pyrimidin-3-yl]acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H18N5O4-
assistant