How get LDAP properties

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C#

LDAP

I connect to ldap server with c#. I want search by propertie- (telephoneNumber=*). But if i insert it to code program show me error.

This code work perfect.

DirectoryEntry searchRoot = null;
            searchRoot = new DirectoryEntry("LDAP://OU=OrgUnit,DC=dgp,DC=hexl,DC=ru");
            DirectorySearcher search = new DirectorySearcher(searchRoot);
            search.Filter = "(&(objectCategory=*)(objectClass=user)))";
           

             SearchResult result;
             SearchResultCollection resultCol = search.FindAll();
            if (resultCol != null)
            {
                for (int counter = 0; counter < resultCol.Count; counter++)
                {
                     result = resultCol[counter];
                }
            }

But i cannot understand make this search query

(&(objectCategory=*)(objectClass=user)(telephoneNumber="222")))