You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-(3,4-dimethoxyphenyl)ethyl]-3-[[2-(3-fluoro-4-methoxyphenyl)acetyl]amino]thiourea is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H24FN3O4S
assistant