how to add book prices automatically on checkbox selection

<input type="checkbox" value="1000"  name="HTML" id="1"  class="box">HTML<br /><br />
<input type="checkbox"  name="C" value="1500" id="2"  class="box">C#<br /><br />
<input type="checkbox"  name="JQuery" value="2000" id="5"  class="box">JQuery<br /><br />
<input type="button" id="GetTotal" value="Get total amount"><br />

$(document).ready(function(){
    $('#GetTotal').on('click', function(){
  var prices = [];
   $('input:checked').each(function() {

       prices .push($(this).attr("value"));

 });
        var total=0;
   for(var i=0;i<prices.length;i++)
   {
    total=total+parseInt(prices [i]);
   }
   alert("Total amount of selected course are:"+total);
   switch(prices.length)
   {
       case 1:
           alert("10% discount");
           break;
       case 2:
           alert("20% discount");
           break;
       case 3:
           alert("30% discount");
           break;
       default:
           alert("Invalid selection");
   }
 });
});