contract ERC20 is IERC20 {
	using SafeMath for uint256;

	mapping (address => uint256) private _balances;

	mapping (address => mapping (address => uint256)) private _allowed;

	uint256 private _totalSupply;

	/**
	* @dev Total number of tokens in existence
	*/
	function totalSupply() public view returns (uint256) {
		return _totalSupply;
	}

	/**
	* @dev Gets the balance of the specified address.
	* @param owner The address to query the balance of.
	* @return An uint256 representing the amount owned by the passed address.
	*/
	function balanceOf(address owner) public view returns (uint256) {
		return _balances[owner];
	}

	/**
	 * @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 specifying the amount of tokens still available for the spender.
	 */
	function allowance(
		address owner,
		address spender
	 )
		public
		view
		returns (uint256)
	{
		return _allowed[owner][spender];
	}

	/**
	* @dev Transfer token for a specified address
	* @param to The address to transfer to.
	* @param value The amount to be transferred.
	*/
	function transfer(address to, uint256 value) public returns (bool) {
		_transfer(msg.sender, to, value);
		return true;
	}

	/**
	 * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
	 * Beware that changing an allowance with this method brings the risk that someone may use both the old
	 * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
	 * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
	 * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
	 * @param spender The address which will spend the funds.
	 * @param value The amount of tokens to be spent.
	 */
	function approve(address spender, uint256 value) public returns (bool) {
		require(spender != address(0));

		_allowed[msg.sender][spender] = value;
		emit Approval(msg.sender, spender, 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 amount of tokens to be transferred
	 */
	function transferFrom(
		address from,
		address to,
		uint256 value
	)
		public
		returns (bool)
	{
		require(value <= _allowed[from][msg.sender]);

		_allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
		_transfer(from, to, value);
		return true;
	}

	/**
	 * @dev Increase the amount of tokens that an owner allowed to a spender.
	 * approve should be called when allowed_[_spender] == 0. To increment
	 * allowed value is better to use this function to avoid 2 calls (and wait until
	 * the first transaction is mined)
	 * From MonolithDAO Token.sol
	 * @param spender The address which will spend the funds.
	 * @param addedValue The amount of tokens to increase the allowance by.
	 */
	function increaseAllowance(
		address spender,
		uint256 addedValue
	)
		public
		returns (bool)
	{
		require(spender != address(0));

		_allowed[msg.sender][spender] = (
			_allowed[msg.sender][spender].add(addedValue));
		emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
		return true;
	}

	/**
	 * @dev Decrease the amount of tokens that an owner allowed to a spender.
	 * approve should be called when allowed_[_spender] == 0. To decrement
	 * allowed value is better to use this function to avoid 2 calls (and wait until
	 * the first transaction is mined)
	 * From MonolithDAO Token.sol
	 * @param spender The address which will spend the funds.
	 * @param subtractedValue The amount of tokens to decrease the allowance by.
	 */
	function decreaseAllowance(
		address spender,
		uint256 subtractedValue
	)
		public
		returns (bool)
	{
		require(spender != address(0));

		_allowed[msg.sender][spender] = (
			_allowed[msg.sender][spender].sub(subtractedValue));
		emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
		return true;
	}

	/**
	* @dev Transfer token for a specified addresses
	* @param from The address to transfer from.
	* @param to The address to transfer to.
	* @param value The amount to be transferred.
	*/
	function _transfer(address from, address to, uint256 value) internal {
		require(value <= _balances[from]);
		require(to != address(0));

		_balances[from] = _balances[from].sub(value);
		_balances[to] = _balances[to].add(value);
		emit Transfer(from, to, value);
	}

	/**
	 * @dev Internal function that mints an amount of the token and assigns it to
	 * an account. This encapsulates the modification of balances such that the
	 * proper events are emitted.
	 * @param account The account that will receive the created tokens.
	 * @param value The amount that will be created.
	 */
	function _mint(address account, uint256 value) internal {
		require(account != address(0));
		_totalSupply = _totalSupply.add(value);
		_balances[account] = _balances[account].add(value);
		emit Transfer(address(0), account, value);
	}

	/**
	 * @dev Internal function that burns an amount of the token of a given
	 * account.
	 * @param account The account whose tokens will be burnt.
	 * @param value The amount that will be burnt.
	 */
	function _burn(address account, uint256 value) internal {
		require(account != address(0));
		require(value <= _balances[account]);

		_totalSupply = _totalSupply.sub(value);
		_balances[account] = _balances[account].sub(value);
		emit Transfer(account, address(0), value);
	}

	/**
	 * @dev Internal function that burns an amount of the token of a given
	 * account, deducting from the sender's allowance for said account. Uses the
	 * internal burn function.
	 * @param account The account whose tokens will be burnt.
	 * @param value The amount that will be burnt.
	 */
	function _burnFrom(address account, uint256 value) internal {
		require(value <= _allowed[account][msg.sender]);

		// Should https://github.com/OpenZeppelin/zeppelin-solidity/issues/707 be accepted,
		// this function needs to emit an event with the updated approval.
		_allowed[account][msg.sender] = _allowed[account][msg.sender].sub(
			value);
		_burn(account, value);
	}
}
/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
 * Originally based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
function decreaseAllowance(
		address spender,
		uint256 subtractedValue
	)
		public
		returns (bool)
	{
		require(spender != address(0));

		_allowed[msg.sender][spender] = (
			_allowed[msg.sender][spender].sub(subtractedValue));
		emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
		return true;
	}
/**
 	 * @dev Decrease the amount of tokens that an owner allowed to a spender.
 	 * approve should be called when allowed_[_spender] == 0. To decrement
 	 * allowed value is better to use this function to avoid 2 calls (and wait until
 	 * the first transaction is mined)
 	 * From MonolithDAO Token.sol
 	 * @param spender The address which will spend the funds.
 	 * @param subtractedValue The amount of tokens to decrease the allowance by.
 	 */