I've got this jQuery to sum all values in "Amount" columns on exiting any of them, updating the "Total" text input with the total:

1.     /* boxAmount1...boxAmount5 - when any of them change, update boxGrandTotal */
       $(document).on("blur", '[id^="boxAmount"]', function (e) {
           var amount1 = $('[id$=boxAmount1]').val();
           var amount2 = $('[id$=boxAmount2]').val();
           var amount3 = $('[id$=boxAmount3]').val();
           var amount4 = $('[id$=boxAmount4]').val();
           var amount5 = $('[id$=boxAmount5]').val();
           var grandtotal = amount1 + amount2 + amount3 + amount4 + amount5;
           $('[id$=boxGrandTotal]').val(grandtotal);
       });

However, it doesn't work, as you can see here:

Here's a jsfiddle showing that even when using parseInt(), the code doesn't work Using jQuery 1.11.0, as I get "NaN" in the grand total box.

What have I overlooked?