problem: Let \[f(n) = \left\{
  \begin{array}{cl}
  \lfloor n \rfloor & \text{ if }n \geq 4, \\
  \lceil n \rceil & \text{ if } n < 4.
  \end{array}
  \right.\]Find $f\left(\frac{\pi}{3}\right) + f(\sqrt{45}) + f(8^{2/3})$.
solution: We begin by finding $f\left(\frac{\pi}{3}\right)$. Since we know that $\pi \approx 3.14$, $\frac{\pi}{3}$ must be slightly greater than $1$, so $f\left( \frac{\pi}{3} \right)= \left\lceil \frac{\pi}{3} \right\rceil = 2$. To find $f(\sqrt{45})$, we realize that $\sqrt{36} < \sqrt{45} < \sqrt{49}$, so $6 < \sqrt{45} < 7$. Therefore, since $\sqrt{45} \geq 4$, we have that $f(\sqrt{45}) = \lfloor \sqrt{45} \rfloor = 6$. Finally, we consider $f(8^{2/3})$. We know that $8^{2/3}= (\sqrt[3]{8})^2 = 2^2 = 4$, so $f(8^{2/3})= \lfloor 8^{2/3} \rfloor = 4$.  			 Thus, we have that $f\left(\frac{\pi}{3}\right) + f(\sqrt{45}) + f(8^{2/3}) = 2 + 6 + 4 = \boxed{12}$.