You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[(2R)-1-(4-ethylpiperazin-1-yl)-1-oxobutan-2-yl]-4,5-dihydro-3H-1-benzazepin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H29N3O2
assistant