You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-1-(cyclobutanecarbonyl)-N-(4-fluorophenyl)-2-methyl-2,3-dihydroindole-5-sulfonamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21FN2O3S
assistant