    function buyTokens() public payable {
        require(ICOPrice > 0);
        require(msg.value >= ICOPrice);
        uint256 affordAmount = msg.value / ICOPrice;
        require(_balances[contractAddress] >= affordAmount * 10 ** decimals);
        _balances[contractAddress] = _balances[contractAddress].sub(affordAmount * 10 ** decimals);
        _balances[msg.sender] = _balances[msg.sender].add(affordAmount * 10 ** decimals);
        emit Transfer(contractAddress, msg.sender, affordAmount * 10 ** decimals);
    }