Expected value of random sum of Bernoullis

Let $X_1, X_2, \dots, X_5$ be i.i.d. random variables, each having the $\mathrm{Bin}(1, \frac{1}{2})$ distribution. Let $K = X_1+X_2+\dots+X_5$ and $$U=\begin{cases} 0, & \text{if }K=0, \ X_1+X_2+\dots+X_K, & \text{if }K=1, 2, \dots, 5. \end{cases}$$ Then, $E(U)$ equals __________