You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-(dimethylamino)-2-(4-ethylphenyl)ethyl]-2-(3,7-dimethyl-2,6-dioxopurin-1-yl)acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H28N6O3
assistant