You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 1-[4-(2-methoxyphenyl)piperidin-1-yl]-3-(4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazin-2-yl)propan-1-one .
user
C21H28N4O2
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