The logic for req_ht near the end is wrong. Here's your code slightly modified: https://mirror.codeforces.com/contest/1709/submission/203607093

Your code is wrong on the right side. Lets say maxi-xs is 4 and k is 3. In this case req_ht should be 6, but your code gives 5. You need k minus what your code has, and then need to account for if maxi-xs mod k is 0.