You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-[4-[1-(4-fluorophenyl)-5-(trifluoromethyl)indol-3-yl]piperidin-1-yl]ethyl]-1-oxidopyrrolidin-1-ium-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C26H27F4N3O2
assistant