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 15-oxahexacyclo[11.7.1.02,11.05,10.014,16.017,21]henicosa-1(20),2,4,7,9,11,13(21),16,18-nonaene ?
user
C20H12O
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