You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[6,7-dichloro-9-(3-hydroxy-3,4-dihydro-2H-1,4-benzoxazin-7-yl)-1,3,4,5-tetrahydropyrido[4,3-b]indol-2-yl]-2-hydroxyethanone by IUPAC nomenclature, provide its molecular formula.
user
C21H19Cl2N3O4
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