You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[(4E,5E)-5-butan-2-ylidene-4-ethylidene-2-methyl-6-oxopyrimidin-1-yl]piperidine-2,6-dione;ethane The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H27N3O3
assistant