You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-ethyl-2-[[4-(4-methoxyphenyl)thiophen-2-yl]methyl]-3-(4-methylsulfonylbutan-2-yl)guanidine is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H29N3O3S2
assistant