function updateTotalPayment()
{
	total_payment = document.getElementById('total_payment');
	
	count = 0;
	for (i=1; ; i++)
	{
		if (document.getElementById('time_slot_'+i) == null) break;
		if (document.getElementById('time_slot_'+i).value != '') count++;
	}
	
	total_payment.value = formatCurrency(200.0 * count);
}

function enableTotalPayment()
{
	document.getElementById('total_payment').disabled = '';
}

function formatCurrency(num)
{
	num = num.toString().replace(/\$|\,/g,'');
	if (isNaN(num)) num = "0";
	sign = (num == (num = Math.abs(num)));
	num = Math.floor(num * 100 + 0.50000000001);
	cents = num % 100;
	num = Math.floor(num / 100).toString();
	if (cents < 10) cents = "0" + cents;
	for (var i = 0; i < Math.floor((num.length - (1 + i)) / 3); i++)
		num = num.substring(0, num.length - (4 * i + 3)) + ',' + num.substring(num.length-(4 * i + 3));
		
	return (((sign)?'':'-') + '$' + num + '.' + cents);
}