You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2-cyclopropyl-7,8-dihydro-5H-pyrido[4,3-d]pyrimidin-6-yl)-[4-(pyrazol-1-ylmethyl)phenyl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21N5O
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