How to decrease maxTxAmount via Web3 on BSCScan to match 0.5% of all supply?

[Babob]

Total Supply: 1,000,000,000,000,000
Decimals: 9

function setMaxTxPercent(uint256 maxTxPercent) external onlyOwner() {
        _maxTxAmount = _tTotal.mul(maxTxPercent).div(
            10**2
        );
    }

Setting this to 1 returns

which is 10,000,000,000,000 (1%).
When I try to input 0.5 bscscan.com returns

invalid number value (arg="maxTxPercent", coderType="uint256", value="0.5")

How to set 0.5% maxTxAmount via web3 on bscscan to match 5000000000000000000000 (5,000,000,000,000) ?