You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (1S,3R,3aS)-1-[(2R,3R)-2-ethyl-4-methyloxolan-3-yl]oxy-3-phenyl-3a,4,5,6-tetrahydro-3H-pyrrolo[1,2-c][1,3,2]oxazaphosphole by IUPAC nomenclature, provide its molecular formula.
user
C18H26NO3P
assistant