This is a problem from Codeforces Round 975. I tried to solve it in the round time and expected to get higher rating. A solution of binary search to this problem jumped out in my mind, and I coded it quickly, but I got WA again and again. Please help me, maybe there are some mathematical wrong int my solution or some bugs in my codes, please pointed it out, thank you!!!!!
You are doing binary search on a non monotone function
Could you explain that why it is a no monotone function?