You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2S,3S,4R,5R)-5-[6-amino-2-[3-[ethyl(methylcarbamoyl)amino]prop-1-ynyl]purin-9-yl]-N-cyclopropyl-3,4-dihydroxyoxolane-2-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C20H26N8O5
assistant