can anyone give me an example for the following metric $d$?

Let $\Omega = \mathbb{N}\_+ \cup \{ \infty \}$ and $d$ be a metric such that all points $n \in \mathbb{N}\_+$ are isolated w.r.t. $d$ and $\lim\_{n \rightarrow \infty} d(n,\infty) = 0$.

Thank you very much!