You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-[4-(2-azabicyclo[2.1.1]hexan-2-yl)spiro[8,9-dihydropurino[8,9-c][1,4]oxazine-6,1'-cyclobutane]-2-yl]pyrimidin-2-amine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H22N8O
assistant