You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[(3-fluorophenyl)methyl]-2-methyl-3-[[4-[(2-oxopyrrolidin-1-yl)methyl]phenyl]methyl]guanidine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H25FN4O
assistant