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-[2-(2-oxo-3H-indol-1-yl)ethyl]-6-azaspiro[2.5]octane-2-carboxamide;hydrochloride is given. What is its corresponding molecular formula?
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C18H24ClN3O2
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