You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-methoxyphenyl)-1-[4-(1,3,5-trimethylpyrazolo[4,3-d]pyrimidin-7-yl)piperazin-1-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H26N6O2
assistant