You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(1S,2R,4R)-7-azabicyclo[2.2.1]heptan-2-yl]-2-(4-methylpiperazin-1-yl)-1-benzothiophene-6-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H26N4OS
assistant