Divide surface in equal parts

I am trying to divide a surface in 3 equal parts.
The problem i’m having is calculating the places where to cut the surface.
With a rectangle its not that hard. But with a shape like shown in my post i cant figure it out.
The parts dont have to look the same. They just need to have the same surface area (it doesn’t have to be exactly equal, just simular)

I tried using surface.getisoline node and enter a percentage, but the node acts like my surface is a square and doesnt actualy show the percentage of the area

Thanks!