Continuity of a piecewise function

A function with domain $x \in [0, \infty)$ has the following rule.

$f(x) = \begin{cases} \dfrac{\left(\sqrt{x} - 2\right)\arctan\left(\dfrac{x}{4}\right)}{x^2 - 3x - 4}, & x \in [0, \infty) \setminus \{4\} \\ p, & x = 4 \end{cases}$

For the function to be continuous on the interval $[0, \infty)$, the value of $p$ must be