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<?phpheader( $_SERVER["SERVER_PROTOCOL"] . ' 404 Not Found');
 ?>
 <h1 style="color: red">URL not found.</h1>
 <?php
 $previous = "javascript:history.go(-1)";
 if(isset($_SERVER['HTTP_REFERER'])) {
 $previous = filter_var($_SERVER['HTTP_REFERER'],FILTER_VALIDATE_URL);
 }
 ?>
 <h3>Please <a href="<?php echo $previous ?>">go back</a> and try again.</h3>
 
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