You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 1-benzothiophen-2-yl-[(1R,2R,4S)-2-ethyl-2-(hydroxymethyl)-7-azabicyclo[2.2.1]heptan-7-yl]methanone into its molecular formula.
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C18H21NO2S
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