<span id="cena">280</span>cena = document.querySelector("#cena");
var classes = [];
$('.input_class').each(function(index){
classes[index] = $(this).val();
};$('.input_class').eq(1).val();
function f() {return 1;}
var sum = 0;
$('.class').on('click', function(e){
var $this = $(this);
if ($this.prop('disabled')) {return false;};
$this.prop('disabled', true);
$this.val('Вы подписаны');
});