How to remove vertical space between divs in Bootstrap 3 grid layout?

How to remove vertical space between divs in Bootstrap 3 grid layout?

My BS3 grid layout renders as follows:

However, I don't want the space between the 1st div (yellow) and the 3rd
div (red).
Here's my code:
<div class='row'>
<div class="col-xs-12 col-sm-6"
style='background-color:yellow;height:100px'>1st div</div>
<div class="col-xs-12 col-sm-6"
style='background-color:blue;height:200px'>2nd div</div>
<div class="col-xs-12 col-sm-6"
style='background-color:red;height:100px'>3rd div</div>
</div>
Any ideas please?