3. Let the function $f_{0}(x)=|x|, f_{1}(x)=\left|f_{0}(x)-1\right|, f_{2}(x)=$ $\left|f_{1}(x)-2\right|$, then the area of the closed part of the figure enclosed by the graph of the function $y=f_{2}(x)$ and the $x$-axis is $\qquad$.
3. Draw the graphs of the functions $y=f_{0}(x)$, $y=f_{1}(x)$, $y=f_{2}(x)$ in sequence (as shown in the figure), the required area is 7.