using System;
using System.Text.RegularExpressions;

public class Test
{
    public static void Main()
    {
        string pattern = @"cn=(?!.*cn=)([^\\]+)";
        string input = @"ou=company\ou=country\ou=site\cn=office\cn=name\ou=pet";

        foreach (Match m in Regex.Matches(input, pattern)) {
            Console.WriteLine("{0}, {1}", m.Value, m.Groups[1].Value);
        }
    }
}