You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-ethyl-2,5-dioxo-4-propan-2-ylimidazolidin-1-yl)-N-(2-phenoxyethyl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H25N3O4
assistant