If element's descendent has class x, add class to element's sibling that has a descendent with class y

I want to check to see if an element has a descendent with a certain class X. If so, I want to check that element's siblings to see if they have a descendent with a class Y. If so, I would like to add class to that sibling with the descendent with a class Y.
HTML:

<div class="x">
    <div>
        <p class="y">Y</p>
    </div>
</div>
<div class="x">
    <div>
        <p class="z">Z</p>
    </div>
</div>

jQuery:

$('div').each(function(){
    if($(this).find('.y')){
      $(this).siblings('div').find('.z').closest('div').addClass(abc);    
    }
});

Here's a fiddle:
http://ift.tt/1JrgAhg

Thanks for any help!