You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-methyl-6-[[(2R,6R)-2-methyl-6-phenylmorpholin-4-yl]methyl]-5H-pyrazolo[3,4-d]pyrimidin-4-one by IUPAC nomenclature, provide its molecular formula.
user
C18H21N5O2
assistant