private int tryGuessNumber(int number) {

        if (number > currentUser.getUpperBound()) {
            return -1;
        }

        if (currentUser.theNumberIs(number)) {
            return number;
        }

        int answer = tryGuessNumber(2 * number);
        if (answer == -1) {
            answer = tryGuessNumber(2 * number + 1);
        }
        return answer;
    }