You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule 2-[(4R)-4-butyl-4-(4-fluorophenyl)-2,5-dioxoimidazolidin-1-yl]-N-[(1S)-1-cyano-1-cyclopropylethyl]acetamide ?
user
C21H25FN4O3
assistant