Let $\displaystyle (s_{n})$ be a sequence such that $\displaystyle |s_{n+1} - s_{n}| < 2^{-n}$ for all $\displaystyle n \in \mathbb{N}$. Prove that $\displaystyle (s_{n})$ is a Cauchy sequence.

How would I exactly go about this? My professor really didn't go over this. All she defined was that a Cauchy sequence is such that given $\displaystyle \epsilon > 0$ there exists $\displaystyle N$ such that if $\displaystyle n,m > N$, then $\displaystyle |s_{n}-s_{m}|< \epsilon$.