You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(2S,3R,4S,5S,6S)-6-acetyl-3-acetyloxy-4,5-dimethyloxan-2-yl]oxy-5-(acetyloxymethyl)benzoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H26O9
assistant