You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-pyridin-4-yl-2-[3-(4,5,6,7-tetrahydrobenzimidazol-1-yl)pyrrolidin-1-yl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H23N5O
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