You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the compound with this IUPAC name 2-amino-9-[(1S,6R,8R,9R,10R,15R,17R,18R)-9,18-difluoro-3,12-dihydroxy-17-(6-methylpurin-9-yl)-3,12-bis(sulfanylidene)-2,4,7,11,13,16-hexaoxa-3lambda5,12lambda5-diphosphatricyclo[13.2.1.06,10]octadecan-8-yl]-1H-purin-6-one ?
user
C21H23F2N9O9P2S2
assistant