window.addEvent('domready', function() {
   var hallenfeld = $('hl');
   var freifeld   = $('fl');
   var linput     = $('laenge');
   var binput     = $('breite');
   recalc();
   binput.addEvent('keyup',function(){
       recalc();
   });
   linput.addEvent('keyup',function(){
       recalc();
   });
 
});

function recalc() {
   var hallenfeld = $('hl');
   var freifeld   = $('fl');
   var linput     = $('laenge');
   var binput     = $('breite');
   var laenge = linput.value;
   var breite = binput.value;
   var qm = (laenge * breite).round(1);
   if (qm) {    
      hallenfeld.innerHTML = "(ab ca. " + (qm * 45).round() + ".- CHF/Mt. für " + qm + "m<SUP>2</SUP>)";
      freifeld.innerHTML = "(ab ca. " + (qm * 20).round() + ".- CHF/Mt. für " + qm + "m<SUP>2</SUP>)";
    } else {
      hallenfeld.innerHTML = "";
      freifeld.innerHTML = "";
   }
}