You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[1-[(2R,4S)-2-methyl-4-[methyl-[(3-methylphenyl)methyl]amino]piperidine-1-carbonyl]pyrazol-3-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28N4O2
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