A quick way to do this is to swim to the inputleft. Add style.css to your style and remove the class span2from your input (use% or a fixed width instead).
.input-append input { float:left; width:10% }
, bootstrap-responsive.css bootstrap.css, .
http://jsfiddle.net/eterpstra/eXVuM/
( "" , < 768px. , , jsFiddle .)