Fatal Error When Trying to Activate WP Smush Pro

Hello. I am unable to activate WP Smush Pro on my website. Getting error :

Fatal error: Cannot redeclare get_plugin_dir() (previously declared in /hermes/bosnaweb20a/b289/ipg.buzzkindcom/wp-content/plugins/wp-smushit/wp-smush.php:118) in /hermes/bosnaweb20a/b289/ipg.buzzkindcom/wp-content/plugins/wp-smush-pro/wp-smush.php on line 116