You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-[(S)-hydroxy(phenyl)methyl]-6,7-dihydro-4H-pyrazolo[1,5-a]pyrazin-5-yl]-4-pyrazol-1-ylbutan-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H23N5O2
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