contract StandardToken is BasicToken, ERC20 {

    mapping (address => mapping (address => uint)) public allowed;


    /**
    * @dev Transfer tokens from one address to another
    * @param _from address The address which you want to send tokens from
    * @param _to address The address which you want to transfer to
    * @param _value uint the amount of tokens to be transferred
    */
    function transferFrom(address _from, address _to, uint _value) public onlyPayloadSize(3 * 32) {
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);

        emit Transfer(_from, _to, _value);
    }

    function approve(address _spender, uint _value) public onlyPayloadSize(2 * 32) {
        require(!((_value != 0) && (allowed[msg.sender][_spender] != 0)));

        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
    }

    function allowance(address _owner, address _spender) public view returns (uint remaining) {
        return allowed[_owner][_spender];
    }

}
/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based oncode by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
function transferFrom(address _from, address _to, uint _value) public onlyPayloadSize(3 * 32) {
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);

    emit Transfer(_from, _to, _value);
}

/**
 * @dev Transfer tokens from one address to another
 * @param _from address The address which you want to send tokens from
 * @param _to address The address which you want to transfer to
 * @param _value uint the amount of tokens to be transferred
 */