You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[(5R)-4-(4-methoxyphenyl)-4'-methyl-2'-phenylspiro[1,3,4-thiadiazole-5,1'-phthalazine]-2-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C25H22N4O2S
assistant