Hello folks on CodeForces. I came across with a problem adapted from a CodeForces problem (one of my seniors, whom I cannot get contact, used it in our exams, and his tutorial is too intricate for me T_T). So I'd appreciate it if any mates recognise this statement and can tell me its source problem.

Thanks in advance! ❤

Statement: There are two multisets $$$A$$$ and $$$B$$$, both initially empty. And there are $$$m$$$ operations, in one of which a pair of two integers $$$(a_i, b_i)$$$ will be added into/deleted from either $$$A$$$ or $$$B$$$. After every operation, find the minimum of $$$\max(a_x+a_y, b_x+b_y)$$$, where $$$x \in A, y \in B$$$.