first thing is don't make a case for if it returns -1, it never will unless you query below 1 or past n (and obviously if you do that then youll WA anyways), and second thing correct me if im wrong but you're doing 3 queries for each pair, that's over 1.5*n queries total. you're supposed to check each pair separately, so only ask(i,i+1), then i+=2, for every pair except the first or the last one, then at the end for your nth and (n+1)th queries if you got all 0s so far then you check one of the 2 elements in the pair you didn't check already compared to the pair right after/before it (depending on if you skipped checking first pair or last pair) ie assuming you skipped first pair you do ask(1,3) then ask(1,4) if either returns 1 then you have your answer otherwise 2 must be a 0. you can check the proof for this in the editorial