You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-[[3-ethoxy-4-(9H-fluoren-9-ylmethoxycarbonylamino)butanoyl]amino]ethylsulfanyl]acetic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C25H30N2O6S
assistant