The last problem of the International Mathematical Olympiad is also extremely difficult for humans.

“uh that is the minimal bound or like the upper bound it's the lower bound of the upper bound then ai kind of sucks at that and so i think um this is why no ai can solve the last problem but it also is super hard for human as well and like if you look at the first five problems you can basically when you look at a problem you already know how to decompose”