You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[(3S)-3-ethyl-4-[(2-methylpropan-2-yl)oxycarbonyl]piperazin-1-yl]benzoic acid by IUPAC nomenclature, provide its molecular formula.
user
C18H26N2O4
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