You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S,4R)-4-[(5S)-5H-imidazo[5,1-a]isoindol-5-yl]-2,2,5,5-tetramethyloxolan-3-ol is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H22N2O2
assistant