You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl (4R,5R)-2-(4-formylpiperazin-1-yl)-4-(3-nitrophenyl)-6-oxo-4,5-dihydro-1H-pyrimidine-5-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H21N5O6
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