You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance 1-[(7-chloro-4-oxopyrido[1,2-a]pyrimidin-2-yl)methyl]-2,3,3a,4,5,6,7,7a-octahydroindole-2-carboxylic acid .
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C18H20ClN3O3
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