You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule (4S)-3-tert-butyl-4-[[4-(1,1-difluoroethyl)phenyl]methyl]-2-oxooxathiazolidin-3-ium-3-carboxylate ?
user
C16H21F2NO4S
assistant