$(function() {
        $('input#user-amount').keyup(function(){
                if (parseInt($(this).val()) > 0) {
                        $('#charged').html('$ ' + Math.round(parseInt($(this).val()) * 1.03));
                        $('#amount').val(Math.round(parseInt($(this).val()) * 1.03));
                } else {
                        $('#charged').html('Please, enter valid amonut');
                }
        });
});
function processPayment(f)
{
        if (f.amount.value > 0 && f.name.value != '') {
                f.item_name.value = "Payment from " + f.name.value + ". " + f.comment.value;
                return true;
        } else {
                alert('Please, fill all required fields.');
                return false;
        }
}