You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (6-amino-4-methylpyridin-3-yl)-[4-(3,5-dimethylpyridin-2-yl)piperazin-1-yl]methanone by IUPAC nomenclature, provide its molecular formula.
user
C18H23N5O
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