Get the latest ID from a SharePoint list

 public int MaximumID()
        {
            SPQuery query = new SPQuery();
            query.Query = "";
            query.RowLimit = 1;
            SPListItemCollection items = SPContext.Current.Site.RootWeb.Lists["ListName"].GetItems(query);
            int maxId = Convert.ToInt32(items[0]["ID"]);
            return maxId;
        }