You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-(4-hydroxy-3-methoxyphenyl)-2-[(E)-3-(3-hydroxy-4-methoxyphenyl)prop-2-enoyl]oxypropanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20O8
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