You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance [(1S)-1-(3,4-difluorophenyl)ethyl]-[2-[2-(2-fluorophenyl)ethylamino]-2-oxoethyl]azanium .
user
C18H20F3N2O+
assistant