contract StandardToken is ERC20Interface {
    using SafeMath for uint256;
    
    string public name;
    string public symbol;
    uint256 public decimals;
    uint256 public totalSupply;
    mapping(address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;

    
    /**
    * @dev Get the totalSupply of the contract
    * @return An uint256 representing the amount of token supplied
    */
    function totalSupply() public view returns(uint256) {
        return totalSupply;
    }
    
    /**
    * @dev Gets the balance of the specified address.
    * @param _owner address The address to query the the balance of.
    * @return An uint256 representing the amount owned by the passed address.
    */
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }

    /**
    * @dev Transfer token for a specified address.
    * @param _to address The address to transfer to.
    * @param _value uint256 The amount to be transferred.
    */
    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));

        // SafeMath.sub will throw if there is not enough balance.
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
    * @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 uint256 the amout of tokens to be transfered.
    */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));

        uint256 _allowance = allowed[_from][msg.sender];

        // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
        // require (_value <= _allowance);

        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = _allowance.sub(_value);
        emit Transfer(_from, _to, _value);
        return true;
    }
    
    /**
    * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
    * @param _spender address The address which will spend the funds.
    * @param _value uint256 The amount of tokens to be spent.
    */
    function approve(address _spender, uint256 _value) public returns (bool) {
        // 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) || (allowed[msg.sender][_spender] == 0));

        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
    /**
    * @dev Function to check the amount of tokens that an owner allowed to a spender.
    * @param _owner address The address which owns the funds.
    * @param _spender address The address which will spend the funds.
    * @return A uint256 specifing the amount of tokens still avaible for the spender.
    */
    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    

}
function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];
}

/**
 * @dev Gets the balance of the specified address.
 * @param _owner address The address to query the the balance of.
 * @return An uint256 representing the amount owned by the passed address.
 */