function exchangePreDGZTokens() stopInEmergency onlyAfterStart public
    {
        uint tokenAmount = tokenRewardPreDGZ.allowance(msg.sender, this);
        require(tokenAmount > 0);
        require(tokenRewardPreDGZ.transferFrom(msg.sender, address(0), tokenAmount));
        uint amountSendTokens = tokenAmount * preDGZtoDGZExchangeRate  / 100000000;
        preBalanceOf[msg.sender] += tokenAmount;
        tokenReward.transfer(msg.sender, amountSendTokens);
    }