Want use 'or' operator whit file_exists php

Question

I want to use or operator in php file_exists() function. I have files whichone name admin_blablabla.php and i also have files withoutadmin 'tag'. I don't use any php framework etc. Does any idea why don't work it?

$page0 is got from $_GET["page"] (f.e: ...index.php?lang=en&page=add_user)

    if ((!file_exists("engine/pages/" . $page[0] . ".php") or (!file_exists("engine/pages/admin_" . $page[0] . ".php"))) && $page[0] != "" && $page[0] != "login" && $page[0] != "logout")  {
        $web_page = "404";
    }