You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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8-[[1-(4-fluorophenyl)-2,5-dimethylpyrrol-3-yl]methylidene]-6,10-dioxaspiro[4.5]decane-7,9-dione is the IUPAC name of a molecule. Please give its molecular formula.
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C21H20FNO4
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