You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named methyl (E)-2-[(2R,3R,12bR)-3-ethyl-1,2,3,4,6,7,12,12b-octahydroindolo[2,3-a]quinolizin-2-yl]-3-methoxyprop-2-enoate by IUPAC nomenclature, provide its molecular formula.
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C22H28N2O3
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