You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S)-1-ethyl-4'-[hydroxy-(4-prop-2-enoxyphenyl)methylidene]-1'-(3-methoxypropyl)spiro[indole-3,5'-pyrrolidine]-2,2',3'-trione is the IUPAC name of a molecule. Please give its molecular formula.
user
C27H28N2O6
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