Variance of a Geometric-Stopped Exponential Sum

Let $N \sim \operatorname{Geometric}(1/2)$ (so $P(N = k) = (1/2)^k$ for $k = 1, 2, \ldots$) and, given $N$, let $X_1, \ldots, X_N$ be i.i.d.\ $\operatorname{Exp}(1)$. Set $S = X_1 + \cdots + X_N$. Using the law of total expectation and Eve's law, find $E[S]$ and $\operatorname{Var}(S)$.