buckling calculation with multiple cross sections

5150racecar

Hello, I couldn't find an answer to this question. I have a long slender cylindrical post with different diameters (largest diameter on the bottom, small diameter on the top with a total of 3 diameter changes) it is not a taper but stepped.

How can I calculate the buckling load for this? There are a lot of examples when the cross section is uniform using pi^2EI/(KL)^2 but nothing for different cross sections. I'm assuming you cannot just do them all individually and sum up the results.

Much help is appreciated!