Answer
$\frac{4}{3}$.
Work Step by Step
We can see that the ratio of subsequent terms is $-\frac{1}{2}$, thus $r=-\frac{1}{2}$.
The sum of an infinte geometric series can be dividing the first term($a_1$) by the difference of $1$ and the common ratio ($r$). So $S=\frac{a_1}{1-r}$.
Hence here $S=\frac{2}{1-(-\frac{1}{2})}=\frac{4}{3}$.
