You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by (1S,4R,5S,6R,7S,8S,11S,12R,13R,14R,15R,16R,20S,21R)-5-methyl-3-oxanonacyclo[10.9.0.01,4.04,8.05,15.06,13.07,11.014,21.016,20]henicosane ?
user
C21H26O
assistant