def get_number_of_usable_hosts_from_raw_address(raw_address: str) -> int:
    """
    Return number of usable host ip addresses.

    >>> get_number_of_usable_hosts_from_raw_address("192.168.1.15/24")
    254
    >>> get_number_of_usable_hosts_from_raw_address("91.124.230.205/30")
    2
    """

    slash_ind = raw_address.index('/')
    prefix = int(raw_address[slash_ind + 1:])
    return pow(2, 32-prefix) - 2