You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 3-amino-N-[4-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-4-oxobutyl]propanamide into its molecular formula.
user
C18H27N3O4
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