You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 1-(2,3-dihydroindol-1-yl)-2-[4-[(2S,4S)-2-methylpiperidine-4-carbonyl]piperazin-1-yl]ethanone;hydrochloride into its molecular formula.
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C21H31ClN4O2
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