You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(2R,4S,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methoxy-[[[(2R,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methoxy-hydroxyphosphoryl]methyl]phosphinic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28N10O12P2
assistant