You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named 5-phenyl-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridine-3-carbonyl)piperazin-2-one is given. What is its corresponding molecular formula?
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C18H20N4O2
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