You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (1S,4S)-2-(4-methylphenyl)sulfonyl-5-phenyl-2-aza-5-phosphabicyclo[2.2.1]heptane by IUPAC nomenclature, provide its molecular formula.
user
C18H20NO2PS
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