You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-butyl-3-[(3-pentyl-4,5,6,7-tetrahydro-1-benzofuran-2-yl)methylidene]-1H-indol-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C26H33NO2
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