You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-methylphenyl)-7-(pyridin-2-ylmethyl)-3,5,6,8-tetrahydropyrido[3,4-d]pyrimidin-4-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20N4O
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