You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named N-[(E)-(3,4-dihydroxyphenyl)methylideneamino]-4-[(2E)-2-[(3,4-dihydroxyphenyl)methylidene]hydrazinyl]benzamide is given. What is its corresponding molecular formula?
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C21H18N4O5
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