You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (1R,2R,3S,4S)-3-[[4-[(2S)-butan-2-yl]phenyl]carbamoyl]-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid into its molecular formula.
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C18H21NO4
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