public void FindStuff() {

    string pattern = @"(=)([A-Z]_)?(\d+|[A-Z_]+)";

    string example1 = "cn=R_PREVADZKOVATEL_IOM,ou=roles,ou=upvs,ou=apps,dc=slovensko,dc=sk";

    foreach (Match match in Regex.Matches(example1, pattern)) {
        Console.WriteLine(match.Groups[3].Value);
    }
}