You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule (6R,7R)-3-ethyl-N-(3-methoxyphenyl)-6-(4-methylphenyl)-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-7-carboxamide .
user
C21H23N5O2S
assistant