You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-[methyl-[2-[(4-methyl-9-oxothioxanthen-1-yl)amino]ethyl]amino]ethylamino]benzoic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C26H27N3O3S
assistant