Expectation from a piecewise cumulative distribution function

Let $X$ be a random variable with the cumulative distribution function

$$F(x)=\begin{cases}0, & x<0,\ \frac x8, & 0\le x<2,\ \frac{x^2}{16}, & 2\le x<4,\ 1, & x\ge4.\end{cases}$$

Then $E(X)$ equals