function addLiquidity(uint256 ethAmount, uint256 btrflyAmount) internal {
    uint256[2] memory amounts = [ethAmount, btrflyAmount];
    uint256 expectedAmount = ICurveCryptoPool(CURVEPOOL).calc_token_amount(
        amounts
    );
    uint256 minAmount = expectedAmount - ((expectedAmount * slippage) / 1000);

    ICurveCryptoPool(CURVEPOOL).add_liquidity(amounts, minAmount);
}
