function replaceImg(id){
    document.getElementById('main_img').setAttribute('height',document.getElementById('medium_img_height_'+id).value);
    document.getElementById('main_img').src=document.getElementById('medium_img_'+id).value;
    document.getElementById('main_a').href=document.getElementById('big_img_'+id).value;
    document.getElementById('main_a_copy').href=document.getElementById('big_img_'+id).value;
    var images=document.getElementById('gallery_img').getElementsByTagName('img');
    for(var i=0;i<images.length;i++){
        images[i].removeAttribute('class');
    }
    
    document.getElementById('small_img_'+id).setAttribute('class','active');
}