contract StdToken is Token {
    // Fields:
    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;
    uint public supply = 0;

    // Functions:
    function transferTo(address _to, uint256 _value) public returns (bool) {
        require(balances[msg.sender] >= _value);
        require(balances[_to] + _value > balances[_to]);

        balances[msg.sender] = safeSub(balances[msg.sender], _value);
        balances[_to] = safeAdd(balances[_to], _value);

        Transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool){
        require(balances[_from] >= _value);
        require(allowed[_from][msg.sender] >= _value);
        require(balances[_to] + _value > balances[_to]);

        balances[_to] = safeAdd(balances[_to], _value);
        balances[_from] = safeSub(balances[_from], _value);
        allowed[_from][msg.sender] = safeSub(allowed[_from][msg.sender], _value);

        Transfer(_from, _to, _value);
        return true;
    }

    function totalSupply() public constant returns (uint256) {
        return supply;
    }

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

    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;
        Approval(msg.sender, _spender, _value);

        return true;
    }

    function allowance(address _owner, address _spender) public constant returns (uint256) {
        return allowed[_owner][_spender];
    }
}
//StdToken
function transferTo(address _to, uint256 _value) public returns (bool) {
    require(balances[msg.sender] >= _value);
    require(balances[_to] + _value > balances[_to]);

    balances[msg.sender] = safeSub(balances[msg.sender], _value);
    balances[_to] = safeAdd(balances[_to], _value);

    Transfer(msg.sender, _to, _value);
    return true;
}

// Functions: