Top level ancestor ID of current page in navigation menu

I want to get the ID of the top level ancestor in the navigation menu.

So I want to do a function that retrieves id of "TLA" from this list:

Menu
 - Submenu
TLA <- Need its id
 - Submenu 1
 - - Submenu 2 <- active

This function echoes exactly what I need, but I actually want to return the value for using it later in a custom function:

add_filter( 'wp_nav_menu_objects', 'get_navigation_menu_root', 10, 2 );

  function get_navigation_menu_root( $sorted_menu_items, $args ) {
      // find the current menu item
    foreach ( $sorted_menu_items as $menu_item ) {
      if ( $menu_item->current ) {
        // set the root id based on whether the current menu item has a parent or not
        $root_id = ( $menu_item->menu_item_parent ) ? $menu_item->menu_item_parent : $menu_item->ID;
        break;
      }
    }

    // find the top level parent
    if ( ! isset( $args->direct_parent ) ) {
      $prev_root_id = $root_id;
      while ( $prev_root_id != 0 ) {
        foreach ( $sorted_menu_items as $menu_item ) {
          if ( $menu_item->ID == $prev_root_id ) {
            $prev_root_id = $menu_item->menu_item_parent;
            // don't set the root_id to 0 if we've reached the top of the menu
            if ( $prev_root_id != 0 ) $root_id = $menu_item->menu_item_parent;
            break;
          } 
        }
      }
    }
    echo $root_id;
    return $sorted_menu_items;
  }
}