how to put 3 in a list by using .each

I have this code

<ul id="mycarousel-1" class="jcarousel-skin-tango">
  <% @portfolios.each_slice(3) do |f| %> 
    <li><% @portfolios.each do |f| %> 
     <%= link_to image_tag(f.image.url(:medium)), image_path(f.image.url()),class: "plus"  %>
  <% end %>
</ul>

How can I put each 3 image in a one list