You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[1-(2,5-dichlorophenyl)sulfonylpiperidin-4-yl]methyl]-3,4-dihydro-1H-isoquinoline is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H24Cl2N2O2S
assistant