CI 2.2.6 subfolder route 403 error

I have the subfolder admin in controllers folder so it looks like this.

controllers
   admin
       sessions
       pages

etc...

The problem is this i want when i enter only admin in url it goes to sessions controller. And i have set this route
$route['admin'] = 'admin/sessions/login';

But when i try to access site_url/admin i get 403 forbidden error. Am i doing something wrong?  

UPDATE
I think i figure out what the problem is.

I have folder in public part that is called admin. And it tries to display content of that folder, instead of calling the controller route.

The whole folder structure is like this:
application/controllers/admin/...
system/
public/index.php
public/admin/csss|js|fonts...

I know that this kind of setup worked for me before, or maybe something similar. What am i doing wrong now?

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