Contract Source Code:

pragma solidity ^0.5.16;

library SafeMath {
    function add(uint a, uint b) internal pure returns (uint) {
        uint c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint a, uint b) internal pure returns (uint) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        require(b <= a, errorMessage);
        uint c = a - b;

        return c;
    }

    function mul(uint a, uint b) internal pure returns (uint) {
        if (a == 0) {
            return 0;
        }

        uint c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    function div(uint a, uint b) internal pure returns (uint) {
        return div(a, b, "SafeMath: division by zero");
    }

    function div(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint c = a / b;

        return c;
    }
}

library Address {
    function isContract(address account) internal view returns (bool) {
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly {codehash := extcodehash(account)}
        return (codehash != 0x0 && codehash != accountHash);
    }
}

interface IERC20 {
    function totalSupply() external view returns (uint);

    function balanceOf(address account) external view returns (uint);

    function transfer(address recipient, uint amount) external returns (bool);

    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint amount) external returns (bool);

    function transferFrom(address sender, address recipient, uint amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);
}

library SafeERC20 {
    using SafeMath for uint;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint value) internal {
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function callOptionalReturn(IERC20 token, bytes memory data) private {
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) {// Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

contract HDUDRedeem {
    using Address for address;
    using SafeMath for uint;
    using SafeERC20 for IERC20;

    address payable public owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    modifier onlyOwner {
        require(msg.sender == owner, "OnlyOwner methods called by non-owner.");
        _;
    }
    function transferOwnership(address payable newOwner) public onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }


    function withdrawFunds(address payable beneficiary, uint withdrawAmount) public onlyOwner {
        require(withdrawAmount <= address(this).balance, "Withdraw amount larger than balance.");
        beneficiary.transfer(withdrawAmount);
    }

    function withdrawHDUD(address payable beneficiary, uint withdrawAmount) public onlyOwner {
        HDUD.safeTransfer(beneficiary, withdrawAmount);
    }

    function() external payable {
        if (msg.sender == owner) {
        }
    }

    event Redeem(address indexed player, uint sentETH, uint getHDUD);

    IERC20 public HDUD = IERC20(0x214b62B3F1D5CC6D049219920D0F333277FC64cf);
    uint public constant HDUD_RATIO = 30;

    mapping(address => address) public refer;
    mapping(address => uint) public redeemLimit;
    mapping(address => uint) public redeemed;

    constructor () public {
        owner = msg.sender;
    }

    function redeem(address _referrer) public payable returns (bool) {
        require(msg.value >= 0.1 ether, 'ETH value less than 0.1');
        require(msg.value <= 10 ether, 'ETH value more than 10');

        uint limit = redeemLimit[msg.sender].add(0.1 ether).sub(redeemed[msg.sender]);
        require(msg.value <= limit, 'redeem value over limit');
        redeemed[msg.sender] = redeemed[msg.sender].add(msg.value);

        if (refer[msg.sender] == address(0)) {
            require(_referrer != msg.sender, "referrer is this address");
            require(_referrer != address(0), "referrer is the zero address");
            refer[msg.sender] = _referrer;
            redeemLimit[_referrer] = redeemLimit[_referrer].add(0.1 ether);
        }
        address referrer = refer[msg.sender];
        require(referrer != address(0), "no refer error");

        uint sentETH = msg.value;
        uint getHDUD = sentETH.mul(HDUD_RATIO);
        HDUD.safeTransfer(msg.sender, getHDUD);
        emit Redeem(msg.sender, sentETH, getHDUD);

        return true;
    }

}