problem: Let \[f(x) = \begin{cases}
  -x^2 - 1 &\text{if }x<0, \\
  2&\text{if }0 \le x< 4, \\
  \sqrt{x}&\text{if }x \ge 4.
  \end{cases}
  \]Find $f(\pi)$.
solution: Since $\pi$ is about 3.14, we use the second case, so $f(\pi) = \boxed{2}$.