Laravel 5 after 3 posts show an add

Hello guys i have declared my posts with variable $lastItems

@if($lastItems->total() > 0)                   
  @foreach($lastItems as $item)
     @include('._posting.items')                                                  
  @endforeach                                    
@else
     @include('errors.emptycontent')
@endif

and i want to add ads after each 3 post, i use something like this

@if($lastItems->total() > 0)                   
  @foreach($lastItems as $item)
     @include('._posting.items')                                                  
  @endforeach  
 @if($item = 3)
    <img src="link" alt="ads">
 @endif                                  
@else
     @include('errors.emptycontent')
@endif

but the problem is, when i try like this it shows the ads after every post not after 3 posts. What i'm doing wrong?

via Chebli Mohamed