A feed stream $(F_1)$ containing components $A$ and $B$ is processed in a system comprising of separation unit and a mixer as shown below in the schematic diagram. The mole fractions of the components $A$ and $B$ are $x_A$ and $x_B$, respectively. If $F_1+F_2=100 \textit{ kg h}^{-1}$, the degrees of freedom of the system is _________.