You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl (E)-4-[(2'S,3S,3'S,4'S)-6-chloro-4'-(3-chlorophenyl)-1'-(cyclopropylmethyl)-3'-nitro-2-oxospiro[1H-indole-3,5'-pyrrolidine]-2'-yl]but-2-enoate is the IUPAC name of a molecule. Please give its molecular formula.
user
C26H25Cl2N3O5
assistant