You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R,3S,4R,5R)-2-[[[(Z)-4-aminobut-2-enyl]-methylamino]methyl]-5-(8-ethyl-6-methylpurin-9-yl)oxolane-3,4-diol The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H28N6O3
assistant