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int64_t GetMinFee(const CTransaction& tx, unsigned int nBytes, bool fAllowFree, enum GetMinFee_mode mode)
{
    // Base fee is either nMinTxFee or nMinRelayTxFee
    int64_t nBaseFee = (mode == GMF_RELAY) ? tx.nMinRelayTxFee : tx.nMinTxFee;

    int64_t nMinFee = (1 + (int64_t)nBytes / 1000) * nBaseFee;

    if (fAllowFree)
    {
        // There is a free transaction area in blocks created by most miners,
        // * If we are relaying we allow transactions up to DEFAULT_BLOCK_PRIORITY_SIZE - 1000
        //   to be considered to fall into this category. We don't want to encourage sending
        //   multiple transactions instead of one big transaction to avoid fees.
        // * If we are creating a transaction we allow transactions up to 1,000 bytes
        //   to be considered safe and assume they can likely make it into this section.
        if (nBytes < (mode == GMF_SEND ? 1000 : (DEFAULT_BLOCK_PRIORITY_SIZE - 1000)))
            nMinFee = 0;
    }

    // This code can be removed after enough miners have upgraded to version 0.9.
    // Until then, be safe when sending and require a fee if any output
    // is less than CENT:
    if (nMinFee < nBaseFee && mode == GMF_SEND)
    {
        BOOST_FOREACH(const CTxOut& txout, tx.vout)
            if (txout.nValue < CENT)
                nMinFee = nBaseFee;
    }

    if (!MoneyRange(nMinFee))
        nMinFee = MAX_MONEY;
    return nMinFee;
}

The Maximum Very Small Inputs Exceeded (20)