<script>
function kjhgs(){
var summa=0;
var go = document.getElementsByClassName('vse');
for (var i = go.value; i++) { summa+=i; }
document.getElementById("klsa").value=summa);}
</script>
<input value="" id="syda">
<select class="vse" onchange="kjhgs();">
<option value="0"></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select class="vse" onchange="kjhgs();">
<option value="0"></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
все равно не выходит:-(