You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3,4-bis[2-[2-[(2R,3R,4S,5S,6R)-3-acetamido-4-acetyloxy-6-ethyl-5-methyloxan-2-yl]oxyethoxy]ethoxy]-5-[2-[2-[(2R,3R,4S,5R,6R)-3-acetamido-6-ethyl-4,5-dimethyloxan-2-yl]oxyethoxy]ethoxy]benzoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C54H87N3O21
assistant