You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[4-[[5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl]methyl]piperazin-1-yl]-thiophen-2-ylmethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H17N5O4S
assistant