You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(7S)-5-(4-bromophenyl)-7-(3-methylphenyl)-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H15BrN4
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