The following figure shows the graph of a continuous function $y=f\left(x\right)$ on the interval $\left[1, 3\right]$. The points $A\mathit{,}\mathit{ }B\mathit{,}\mathit{ }C$ have coordinates $\left(1, 1\right), \left(3, 2\right) \text{and} \left(2, 3\right)$, respectively, and the lines $L_1$ and $L_2$ are parallel, with $L_1$ being tangent to the curve at $C$. If the area under the graph of $y=f\left(x\right)$ from $x=1$ to $x=3$ is $4$ square units, then the area of the shaded region is: