You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4S,6S,8E,11S)-4,6,15-trihydroxy-11,17-dimethyl-12-oxa-2-azabicyclo[12.4.0]octadeca-1(14),8,15,17-tetraene-3,7,13-trione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H21NO7
assistant