You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule (E)-9-[6-amino-2-(2-methoxyethoxy)-8-oxo-7H-purin-9-yl]-3-methylidenenon-7-enoic acid;ethane into molecular formula.
user
C20H31N5O5
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