You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the compound with this IUPAC name N-methyl-2-[1'-(thiophen-3-ylmethyl)spiro[1,2-dihydroindene-3,4'-piperidine]-1-yl]acetamide ?
user
C21H26N2OS
assistant