Problem: Find the leading order WKB approximation for the specific differential equation: $\epsilon y''' + y = 0$ with initial conditions at $y(0) = 1, y(\epsilon^{1/3}) = e^{-1}, y(-\epsilon^{1/3}) = e^{1} $ where $\epsilon$ is a small positive parameter ($0 < \epsilon \ll 1)$. Give your final answer in a \boxed latex environment.
Solution: $\boxed{e^{\frac{-x}{\epsilon^{1/3}}}}$