You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[[4-(carbamoylamino)-6-methyl-2,5-dioxocyclohex-3-en-1-ylidene]amino]anilino]butanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H21N5O4
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