How to use SharePoint Client Object Model to get User Information by User Lookup ID

protected string getUserEmail(int lookupid)

{

    String Useremail = string.Empty; 

    try

    {

        using (ClientContext clientContext = new ClientContext(siteUrl))

        {

            Microsoft.SharePoint.Client.ListItem userInfo = clientContext.Web.SiteUserInfoList.GetItemById(lookupid);

            clientContext.Load(userInfo);

            clientContext.ExecuteQuery();

            Useremail = userInfo["EMail"].ToString();

        } 

    }

    catch (Exception ex)

    {

        // TODO: // handle the error             

    } 

    return Useremail;

}