Get the first OU in distinguished name string.

GetFirstOU.txt

string GetFirstOU(string dn)
{
    var firstOU = dn.Split(',')
                        .FirstOrDefault(x => x.StartsWith("ou=", StringComparison.OrdinalIgnoreCase));

    if (string.IsNullOrEmpty(firstOU)) return null;

    var result = Regex.Replace(firstOU, Regex.Escape("ou="), "".Replace("$", "$$"), RegexOptions.IgnoreCase);
    return result;
}