def get_next_ip(ip_address, step):
    """
    Calculates the IP address
    through 'step' from the initial address
       get_next_ip("192.168.1.16", 4) -> "192.168.1.20"
    """
    ip_parts = ip_address.split(".")
    return ".".join(ip_parts[:3] + [str(int(ip_parts[3]) + step)])