You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Under IUPAC nomenclature, a molecule named N-[4-[4-(3-cyanopyridin-2-yl)piperazin-1-yl]-4-oxobutan-2-yl]benzamide is given. What is its corresponding molecular formula?
user
C21H23N5O2
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