You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5,7-dimethyl-1'-propan-2-ylspiro[1,3-diazatricyclo[3.3.1.13,7]decane-2,3'-indole]-2',6-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H25N3O2
assistant