You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-methyl-7-(4-morpholin-4-ylphenyl)-5-pyrazolidin-1-ylpyrido[4,3-d]pyrimidin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24N6O2
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