$4$ is an interesting number. What is the most concise way of expressing $256$ using only the number $4$, excluding $4^4$ and the mathematically equivalent $\displaystyle \frac{1}{\frac{1}{4^4}}$, $4 \cdot 4 \cdot 4 \cdot 4$ or $\displaystyle \frac{1}{\frac{1}{4 \cdot 4 \cdot 4 \cdot 4}}$? You are limited to addition, subtraction, multiplication, division and exponents.