APPENDOR-Why WA?

Problem: Append for OR (APPENDOR Problem | CodeChef).
I have tried to solve this problem several times but it is showing me wrong answer. I don’t know why this is happening.
My solution: CodeChef | Competitive Programming | Participate & Learn
Can anyone help me to find out the reason for what the solution is showing WA?

Thanks in advance.

Your code gets WA in this test case

1
1 0
1

The reason for this bug is that __builtin_popcountll(y) =0 and the while loop does not even enter, much less set b=1.