You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-(dimethylamino)-2-(4-fluorophenyl)ethyl]-2-(3-oxo-4H-1,4-benzothiazin-2-yl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H22FN3O2S
assistant