abstract algebra – Get a unit in the ring of the integral group $ mathbb {Z}[mathbb{Z}/5mathbb{Z}]$

Get a non-trivial unit of the entire group ring $ mathbb {Z}[mathbb{Z}/5mathbb{Z}]$. By non-trivial, I do not mean a group element.

Since, bruteforce does not seem possible here, I tried to guess what a unit should be, other than the elements of the group. But I failed in this attempt. I would appreciate any kind of help.

Thank you!