You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule N-[[5-(quinolin-6-ylmethyl)-6,7-dihydro-4H-pyrazolo[1,5-a]pyrazin-2-yl]methyl]methanesulfonamide into molecular formula.
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C18H21N5O2S
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