You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-2-(3,4-dihydroxyphenyl)-7-hydroxy-5-[(2R,3R,4S,5S,6R)-2,4,5-trihydroxy-6-(hydroxymethyl)oxan-3-yl]oxy-2,3-dihydrochromen-4-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22O11
assistant