Mean Absolute Normal

Suppose that $X_i \sim N(0,\sigma_i^2)$, $1 \leq i \leq n$, are independent random variables. Define $\displaystyle \overline{X_n} = \left|\dfrac{1}{n}\sum_{i=1}^n X_i\right|$. Compute $\mathbb{E}\left[ X_n \right]$ when $n = 8$ and $\sigma_i^2 = i$. Round to the nearest thousandth.