CSES Multiplication Table

Would anyone like to share their solution to CSES Multiplication Table? There’s no solution for it in USACO guide, and I can’t see how binary search could be applied. Thanks in advance!

Define f(x) = the number of numbers in the table that is less than or equal to x

You simply want to find the least number such that f(x) >= (n * n + 1) / 2 (this can be done with a binary search)

Try to think about how to calculate f(x) in O(n).

that is the part I struggled with

Actually I got it now, the mention of O(n) really helped.

Can you post your solution? I am still struggling with this problem.