function pridejKus(item) {
    old_value = eval(document.getElementById(item).value);
	document.getElementById(item).value = old_value + 1;
	sectiVse(1);
}

function uberKus(item) {
    old_value = eval(document.getElementById(item).value);
	if (old_value>0) {
			document.getElementById(item).value = old_value -1;
			sectiVse(-1);
	}
}

function sectiVse(new_value) {
   old_total = eval(document.getElementById('total-products').value);
   document.getElementById('total-products').value = old_total + new_value;
}