You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(6S,9aS)-N-benzyl-8-[(2,4-difluorophenyl)methyl]-2-(fluoromethyl)-4,7-dioxo-6-phenyl-3,6,9,9a-tetrahydropyrazino[2,1-c][1,2,4]triazine-1-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C28H26F3N5O3
assistant