The $p$-adic integers as final coalgebra

We express the classical $p$-adic integers $\hat{\mathbb{Z}_p}$, as a metric space, as a final colagebra to a certain endofunctor. We realize the addition and the multiplication on $\hat{\mathbb{Z}_p}$ as the coalgebra maps from $\hat{\mathbb{Z}_p} \times \hat{\mathbb{Z}_p}$.