You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
carbanide;(4Z)-2,3-dimethylhexa-2,4-diene;2,3,4,5-tetramethylhexa-2,4-diene;yttrium is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H41Y34-3
assistant