def fee_calculator(transaction_input=1, transaction_output=1):
    """
    Bitcoin fee calculator.

    :param transaction_input: transaction input numbers, defaults to 1.
    :type transaction_input: int
    :param transaction_output: transaction output numbers, defaults to 1.
    :type transaction_output: int
    :returns: int -- bitcoin fee.

    >>> from shuttle.providers.bitcoin.utils import fee_calculator
    >>> fee_calculator(2, 9)
    1836
    """
    transaction_input = (transaction_input - 1) * 444 + 576
    transaction_output = (transaction_output - 1) * 102
    return transaction_input + transaction_output
