void Insert(struct flight_info* info)
{
    if(head == NULL)
    {
        head = info;
    }
    else
    {
        struct flight_info* curr = head;
        while(curr->next != NULL)
           curr = curr->next;

        curr->next = info;
        info->prev = curr;
        info->next = head;
        head->prev = info;
    }
}