You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4S,9S,13R,16S)-5',7,9,13,19-pentamethylspiro[5-oxapentacyclo[10.8.0.02,9.04,8.013,18]icos-18-ene-6,2'-oxane]-16-ol The above is the IUPAC name of a molecule. Write its molecular formula.
user
C28H44O3
assistant