Include engine/start.php into external PHP file

How can i include engine/start.php into external PHP file.
Example:

File Structure
index.php
elgg folder
data folder

index.php code : 

<?php

require_once('elgg/engine/start.php');

echo "this is index dot php";
?>
require_once gives an error " Failed opening required 'engine/start.php'"

How to include engine/start.php into external php file ?
 

Beginning Developers

Beginning Developers

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