You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[(1S,2S,3R,14R,16S,18R)-18-methyl-19-oxa-12-aza-18-azoniahexacyclo[14.3.1.02,14.03,18.05,13.06,11]icosa-5(13),6,8,10-tetraen-1-yl]ethanone;iodide by IUPAC nomenclature, provide its molecular formula.
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C20H23IN2O2
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