The number of points of non-differentiability of function $\mathrm{f}\left(\mathrm{x}\right)=max\left\{{\sin }^{-1}|\sin \mathrm{x}|,{\cos }^{-1}|\sin \mathrm{x}|\right\},0<\mathrm{x}<2\mathrm{\pi }$ , is ______ .