You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule (4aS,5S,8aR)-2,3,4a,8a-tetrachloro-6-ethenyl-5-[2-(4-hydroxy-3-methoxyphenyl)ethenyl]-5,8-dihydronaphthalene-1,4-dione ?
user
C21H16Cl4O4
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