LIST *del_group_element(LIST *lst)
{
  LIST *curr=lst;

  if ( curr == 0) return;

  do
  {
    int num = curr->number;
    LIST *prev = curr;
    LIST *pos  = curr->next;
    int delete_flag = 0;
    while (pos != 0)
    {
      if (pos->number == num)
      {
        LIST* tmp = pos;
        pos = pos->next;
        prev->next = pos;
        delete tmp;
        delete_flag = 1;
      }
      else
      {
        prev = pos;
        pos  = pos->next;
      }
    }

    if (delete_flag)
    {
      LIST* tmp = curr;
      curr = curr->next;
      delete tmp;
    }
    else
      curr = curr->next;

  } while (curr != 0);

}