jQuery(function($){

$('.small_plan_img img').click(function(){
    var bigImgSrc = '../images/gallery/' + $(this).attr('src').split('/').reverse()[0];
    $('.big_plan_img').fadeOut('100', 
        function(){
            $('.big_plan_img img').attr('src', bigImgSrc);
        }).fadeIn('100');
    $('.small_plan_img a').removeClass('active');
    $(this).parent('a').addClass('active');
    $('#plan_title').text($(this).attr('alt'));
});

});