Let S be the set of points where the functions f (x)= $\left|2-\left|x-3\right|\right|,$ x $\in$R , is not differentiable. Then $\underset{x\in s}{\sum f\left(f\left(x\right)\right)}$ is equal to

$$\begin{gathered} \mathrm{f}\left(\mathrm{x}\right)=\left|2-\left|\mathrm{x}-3\right|\right|, \mathrm{x}\in \mathrm{R} \\ \mathrm{is} \mathrm{not} \mathrm{differentiable} \\ \mathrm{if} |\mathrm{x}-3|=0 \mathrm{and} 2-\left|\mathrm{x}-3\right|=0 \\ \Rightarrow \mathrm{x}=3 and|\mathrm{x}-3|=2 \\ \Rightarrow \mathrm{x}-3=2, -2 \\ \Rightarrow \mathrm{x}=5,1 \\ \therefore \mathrm{s}=\{1,3,5\} \\ \mathrm{f}\left(1\right)=|2-2|=0\Rightarrow \mathrm{f}\left(\mathrm{f}\right(0\left)\right)=\mathrm{f}\left(0\right)=1, \\ \mathrm{f}\left(3\right)=|2-0|=2\Rightarrow \mathrm{f}\left(\mathrm{f}\right(2\left)\right)=\mathrm{f}\left(2\right)=1, \\ and \mathrm{f}\left(5\right)=|2-2|=0\Rightarrow \mathrm{f}\left(\mathrm{f}\right(5\left)\right)=\mathrm{f}\left(0\right)=1 \\ \underset{\mathrm{x}\in 5}{\Rightarrow \sum }\left(\mathrm{f}\left(\mathrm{x}\right)\right)=3 \end{gathered}$$