You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule (7S)-7-[2-(4-chlorophenyl)ethylamino]-2-(4-fluorophenyl)-6,7-dihydro-5H-pyrazolo[1,5-a]pyrazin-4-one ?
user
C20H18ClFN4O
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