You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule [2-cyano-4-[4,5-dihydroxy-6-(hydroxymethyl)-5-methyloxan-2-yl]oxybut-2-enyl] 3-(3,4-dihydroxyphenyl)prop-2-enoate ?
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C21H25NO9
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