f(x) = \left\{ \begin{array}{ccl}
0 & \!\!\!\!\! , & x \in \langle -\infty, 0] \cup [1, 2] \cup [4, +\infty \rangle \\
\frac{1}{2} & \!\!\!\!\! , & 0 < x < 1 \\
\frac{1}{4} & \!\!\!\!\! , & 2 < x < 4
\end{array} \right.