The greatest integer finction, $f(x)=\lfloor x\rfloor$, is defined to be the greatest integer less than or equal to $x$, where $x$ is any real number. For example, $\lfloor 3\rfloor=3,\lfloor 1.999\rfloor=1,\left\lfloor\frac{1}{4}\right\rfloor=0$, and $\lfloor-4.5\rfloor=-5$. Sketch the graph of this function for $-3.5 \leq x \leq 3.5$. Use your sketch to determine the values of $x$ at which discontinuities occur.