Limit Char Over Two Textarea Boxes?

I have a form where users can enter text in one or two textareas. If they only enter text in of of the textareas I can limit the max char to 300 using this:

<script type="text/javascript">
var maxL=300;//nr of max permited characters
function limit(obj){
var nr= document.getElementById('nrc')
var v = new String();
s = obj.value.split('');
for(i=0;i<maxL;i++){v += s[i]}
if(s.length>=maxL){
obj.value=v;
nr.firstChild.data = maxL-v.length;
}
else{nr.firstChild.data = maxL-s.length;}
}
onload=function(){
document.getElementById('nrc').firstChild.data=maxL;
}
</script>

Is there a way that I can limit the total char between the two textareas i.e. If a user enters 180 in the first one they can only enter 120 in the second one.