You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named N-[1-oxo-1-[4-(2-phenylethyl)piperidin-1-yl]propan-2-yl]thiophene-2-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C21H26N2O2S
assistant