[ksa]

хм

Каюсь, не проверял...

<div class="pdf" style="width: 100px;"></div>
<div class="pdf" style="width: 200px;"></div>
<div class="pdf" style="width: 300px;"></div>
<div class="pdf" style="width: 400px;"></div>
<div class="pdf" style="width: 5px;"></div>
<script>
var o = document.getElementsByClassName('pdf');
var max=0;
for (var i = 0; i < o.length; ++i) {
	var val = o[i].style.width.replace('px', ''); 
	if (-val<-max) max=val;
};
alert(max);