system/application/config/routes.php :
$route['^(?!<otherController1>|<otherController2>).*'] = "users/user/$1";
, <otherController1>|<otherController1> , :
$route['^(?!welcome|post).*'] = "users/user/$1";
, Users , . :
$route['user/subscribe'] = "user/subscribe";
$route['user/username_exists'] = "user/username_exists";
$route['user/email_exists'] = "user/email_exists";
$route['user/signup'] = "user/signup";