You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by 1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-2-yl-(2,3,6-trimethylquinolin-4-yl)methanone ?
user
C21H27N3O
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