You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(2,4-difluorophenyl)-3-(2-methyl-2,3-dihydroindol-1-yl)-1,2,4-triazin-5-amine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H15F2N5
assistant