Php include file in different folder that includes another file

I am new in PHP and I've been trying to make a file (index.php) include another file (connect.php) that includes another file (config.php) but they are located in different folders.

This is my directory structure:

 > index.php (in the [root]...)
 > connect.php ([root]/admin/)
 > config.php ([root]/admin/)

This is what I have so far:

index.php

include './admin/connect.php'

connect.php

$directory = getcwd();
chdir(__DIR__);
include "config.php";
chdir($directory);

This is actually working but somehow I'm not loving the idea of changing the working directory.

Is there a better way to achieve my goal?