How to get Initial texture in Post-Processing Stack v2

Hello. I'm trying to write a custom post-processing shader with new **Post-Processing Stack v2**. I already have a few effects in my pipeline, but I need to determine whether I apply them or not based on condition.

So, I need to obtain the initial **source texture right from camera**, before all effects were applied and return it's value if I need.

The logic is to have the mask layer, camera that renders this layer into a texture and post-effect for masking.

Thanks a lot.