public static void main(String[] args) {
    Matcher m = Pattern .compile("^(.*?[.].*?[.].*?[.].*?)[.].*")
                        .matcher(
                                "com.SEM.Google.Generico.space.test");
    if (m.matches()) {
        System.out.println(m.group(1));
    }
}

$project: {
    pathString: {
        $substr: ["$path.dv", 0, 23]
    }

}