3. Let the function $f_{0}(x)=|x|, f_{1}(x)=\left|f_{0}(x)-1\right|, f_{2}(x)=\mid f_{1}(x)$ $-2 \mid$, 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.