You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5Z)-5-[[7-methyl-2-(2-methylpropylamino)-4-oxopyrido[1,2-a]pyrimidin-3-yl]methylidene]-3-(2-methylpropyl)-2-sulfanylidene-1,3-thiazolidin-4-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H26N4O2S2
assistant