How to get Domain account name when the Display name is given

Scenario
Sometimes we may need to get the domain account name from the directory where we give the display name as input.
Code

using System.Text.RegularExpressions;
using System.DirectoryServices;
public static string GetDomainAccountName(string displayName)
{
DirectoryEntry entry = new DirectoryEntry();
entry.Path = "GC://domain.self.com/dc=hi,dc=self,dc=com";
entry.AuthenticationType = AuthenticationTypes.Secure;
entry.Username = "me\\username";
entry.Password = "password";
string[] fullName = displayName.Split(','); //name in format LastName, Firstname
DirectorySearcher search = new DirectorySearcher(entry);
search.Filter = string.Format("(&(objectClass=user)(objectCategory=Person)(&(givenName={0})(sn={1})))", fullName[1].Trim(), fullName[0].Trim());
search.PropertiesToLoad.Add("mail"); // Email Address
search.PropertiesToLoad.Add("givenName"); // First Name
search.PropertiesToLoad.Add("sn"); // Last Name
search.PropertiesToLoad.Add("l"); // City
search.PropertiesToLoad.Add("st"); // State
search.PropertiesToLoad.Add("co"); // Country
search.PropertiesToLoad.Add("postalCode"); // PostalCode
search.PropertiesToLoad.Add("SAMAccountName"); //AccountName
search.PropertiesToLoad.Add("distinguishedName"); //DomainName
// Search for the specified user.
SearchResult result = search.FindOne();
if (result != null) // User found
{
string userEmailAddress = GetProperty(result, "mail");
string userFirstName = GetProperty(result, "givenName");
string userLastName = GetProperty(result, "sn");
string userCity = GetProperty(result, "l");
string userState = GetProperty(result, "st");
string userCountry = GetProperty(result, "co");
string userPostalCode = GetProperty(result, "postalCode");
string userName = GetProperty(result, "SAMAccountName");
string userD = GetProperty(result, "distinguishedName");
Regex regex = new Regex("(?<=DC=).+?(?=,)");
Match match = regex.Match(userD);
string domain = match.Groups[0].Value;
return domain + "\\" + userName;
}
return string.Empty;
}
public static string GetProperty(DirectoryEntry searchResult, string PropertyName)
{
if (searchResult.Properties.Contains(PropertyName))
{
return searchResult.Properties[PropertyName][0].ToString().ToLower();
}
else
{
return string.Empty;
}
}
public static string GetProperty(SearchResult searchResult, string PropertyName)
{
if (searchResult.Properties.Contains(PropertyName))
{
return searchResult.Properties[PropertyName][0].ToString();
}
else
{
return string.Empty;
}
}

Thanks