You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (2S)-N-(4-chlorophenyl)-2-(1,2,3,4-tetrahydroisoquinolin-2-ium-2-yl)propanamide by IUPAC nomenclature, provide its molecular formula.
user
C18H20ClN2O+
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