You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[3-[[6-methyl-3-(7-methyl-5H-pyrrolo[2,3-b]pyrazin-2-yl)pyridin-2-yl]amino]piperidin-1-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H24N6O
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