function convert() {
    var exchangeForm = document.forms["exchange"];
    var resultEl = exchangeForm["res"];
    var sumEl = exchangeForm["sum"];
    
    var sum = sumEl.value;
    var curr = document.getElementsByName("curr")[0].checked ? "EUR" : "USD";
    if (curr != null && sum != null && sum != "" && (sum = parseFloat(sum.replace(',', '.'))) > 0.0) {
        resultEl.value = 'Przeliczam...';
        new Request.HTML({ 
            url: 'kursy.html', 
            onComplete: function(responseTree, responseElements, responseHTML, responseJavaScript) {
                var rate = 0.0;
                responseElements.each(function(element) { 
                    if (element.get('html') == ('1 ' + curr)) {
                        rate = parseFloat(element.getParent().getLast().get('html').replace(',', '.'));
                    }
                });
                if (rate > 0.0) {
                    var res = sum * rate;
                    resultEl.value = res.toFixed(2).replace('.', ',');
                } else {
                    resultEl.value = "Błąd.";
                }
                //resultEl.value = $(exchangeForm).
            } 
        }).get();
    } else {
        //sumEl.value = "";
        resultEl.value = "Podaj kwotę."
    }
}