You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule 2-[3-[[1-[(2-chlorophenyl)methyl]-2,5-dioxoimidazolidin-4-ylidene]methyl]indol-1-yl]acetamide into molecular formula.
user
C21H17ClN4O3
assistant