You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[1-(3-chloro-4-methylphenyl)-2,5-dioxopyrrolidin-3-yl]-methylamino]-N-(3-fluorophenyl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H19ClFN3O3
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