You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 4-ethyl-4-formyloxy-3-[(E)-3-hydroxybut-2-en-2-yl]-9-methylidenetricyclo[6.2.1.01,5]undecane-2-carboxylic acid into its molecular formula.
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C20H28O5
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