Does Viber app have a menu to close the app? I would like to use Viber only if I need it. I want to turn it off if I do not use it, regardless if I can be reached or not. 

I do not wish to have a program running and using energy all the time. However, I can't seem to find any close menu to kill the app. Does it even have a close menu / function?
Just installed Viber on my Samsung Galaxy S4 (Android 4.2.2), and I can find an exit menu via More Options &gt; Exit.