On what interval is the function continuous? $($Enter your answer using interval notation. Enter EMPTY for the empty set.$)$

$f(x)=\{\begin{array}{ccc}0& ifxis\text{i}\text{r}\text{r}\text{a}\text{t}\text{i}\text{o}\text{n}\text{a}\text{l}& \\ 1& ifxis\text{r}\text{a}\text{t}\text{i}\text{o}\text{n}\text{a}\text{l}& \end{array}$