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Translate the chemical IUPAC name 1-[(2R,3'S)-5-(2,5-difluorophenyl)-3'-propylspiro[1,3,4-thiadiazole-2,4'-2,3-dihydrochromene]-3-yl]-2-fluoroethanone into its molecular formula.
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C21H19F3N2O2S
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