Expected gap between two normals

Let $X \sim \mathcal N(0,1)$ and $Y \sim \mathcal N(0,4)$ be independent. Compute $\mathbb{E}\,|Y - X|$. The answer has the form $\left(\dfrac{K}{\pi}\right)^{b}$ for rational $K$ and $b$; report $b\cdot K$.