static long xorSequence(long l, long r) {
        long lsum = getXorSumAt(l-1);
        long rsum = getXorSumAt(r);
        return lsum ^ rsum;
    }
    
    static long getXorSumAt(long i) {
        long rem = i % 8;
        if (rem == 0 || rem == 1) return i;
        if (rem == 2 || rem == 3) return 2;
        if (rem == 4 || rem == 5) return i + 2;
        return 0;
    }