You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule tert-butyl (2R,3S,4aS,10bS)-2,3-dihydroxy-2,3,4,4a,6,10b-hexahydro-1H-phenanthridine-5-carboxylate into molecular formula.
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C18H25NO4
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