pragma solidity ^0.4.18;

contract SafeMath {

    function SafeMath() {
    }

    function safeAdd(uint256 _x, uint256 _y) internal returns (uint256) {
        uint256 z = _x + _y;
        assert(z >= _x);
        return z;
    }

    function safeSub(uint256 _x, uint256 _y) internal returns (uint256) {
        assert(_x >= _y);
        return _x - _y;
    }

    function safeMul(uint256 _x, uint256 _y) internal returns (uint256) {
        uint256 z = _x * _y;
        assert(_x == 0 || z / _x == _y);
        return z;
    }

}

contract TDT is SafeMath {
    string public constant standard = 'Token 0.1';
    uint8 public constant decimals = 18;

    // you need change the following three values
    string public constant name = 'Tiens Doctor Token';
    string public constant symbol = 'TDT';
    uint256 public totalSupply = 0.3 * 10**8 * 10**uint256(decimals);

    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    function TDT() public {
        Transfer(0x00, msg.sender, totalSupply);
        balanceOf[msg.sender] = totalSupply;
    }

    function transfer(address _to, uint256 _value)
    public
    returns (bool success)
    {
        balanceOf[msg.sender] = safeSub(balanceOf[msg.sender], _value);
        balanceOf[_to] = safeAdd(balanceOf[_to], _value);
        Transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value)
    public
    returns (bool success)
    {
        allowance[_from][msg.sender] = safeSub(allowance[_from][msg.sender], _value);
        balanceOf[_from] = safeSub(balanceOf[_from], _value);
        balanceOf[_to] = safeAdd(balanceOf[_to], _value);
        Transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value)
    public
    returns (bool success)
    {
        // To change the approve amount you first have to reduce the addresses`
        //  allowance to zero by calling `approve(_spender, 0)` if it is not
        //  already 0 to mitigate the race condition described here:
        //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
        require(_value == 0 || allowance[msg.sender][_spender] == 0);
        allowance[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    // disable pay ETH to this contract
    function () public payable {
        revert();
    }
}