function transferTokensTo(address to, uint256 givenTokens) private returns (uint256) {
        var providedTokens = givenTokens;
        if (givenTokens > leftTokens) {
            providedTokens = leftTokens;
        }
        leftTokens = leftTokens.sub(providedTokens);
        require(token.manualTransfer(to, providedTokens));
        return providedTokens;
    }