You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 2-(2-fluorophenyl)-1-[(3R)-3-(5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-2-yl)piperidin-1-yl]ethanone .
user
C20H23FN4O
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