contract ERC20Token is ERC20Interface{

    // account balances
    mapping(address => uint256) balances;

    // Owner of account approves the transfer of amount to another account
    mapping(address => mapping (address => uint256)) allowed;

    // Function to access acount balances
    function balanceOf(address _owner) public constant returns (uint256) {
        return balances[_owner];
    }

    // Transfer the _amount from msg.sender to _to account
    function transfer(address _to, uint256 _amount) public returns (bool) {
        if (balances[msg.sender] >= _amount && _amount > 0
                && balances[_to] + _amount > balances[_to]) {
            balances[msg.sender] -= _amount;
            balances[_to] += _amount;
            Transfer(msg.sender, _to, _amount);
            return true;
        } else {
            return false;
        }
    }

    // Send _value amount of tokens from address _from to address _to
    // The transferFrom method is used for a withdraw workflow, allowing contracts to send
    // tokens on your behalf, for example to "deposit" to a contract address and/or to charge
    // fees in sub-currencies; the command should fail unless the _from account has
    // deliberately authorized the sender of the message via some mechanism; we propose
    // these standardized APIs for approval:
    function transferFrom(
        address _from,
        address _to,
        uint256 _amount
    ) public returns (bool) {
        if (balances[_from] >= _amount
            && allowed[_from][msg.sender] >= _amount && _amount > 0
                && balances[_to] + _amount > balances[_to]) {
            balances[_from] -= _amount;
            allowed[_from][msg.sender] -= _amount;
            balances[_to] += _amount;
            Transfer(_from, _to, _amount);
            return true;
        } else {
            return false;
        }
    }

    // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
    // If this function is called again it overwrites the current allowance with _value.
    function approve(address _spender, uint256 _amount) public returns (bool) {
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);
        return true;
    }

    // Function to specify how much _spender is allowed to transfer on _owner's behalf
    function allowance(address _owner, address _spender) public constant returns (uint256) {
        return allowed[_owner][_spender];
    }

}
// Implementation of ERC20Interface
function allowance(address _owner, address _spender) public constant returns (uint256) {
    return allowed[_owner][_spender];
}

// Function to specify how much _spender is allowed to transfer on _owner's behalf