private int lookup(int left, int right) {
        if (found) {
            return 0;
        }
        if (user.theNumberIs(left)) {
            found = true;
            return left;
        }
        if (user.theNumberIs(right)) {
            found = true;
            return right;
        }
        if (left == right || left + 1 == right) {
            return 0;
        }

        int half = (right - left) / 2;

        return lookup(left, left + half) + lookup(left + half + 1, right);
    }