What is the inlet size for my catalytic converter?

I have a 1997 chevrolet monte carlo ls that needs a new catalytic converter to pass emissions. I need to know the inlet size of the catalytic converter so that I can buy the right part. Yes I know there are direct fit parts out there but those cost too much and are nearly absent for my specific car. I'm going to run a catco highflow converter on my car and I need the specific inlet size so I can get the right part, I don't care about the stock outlet because I'm also replacing the muffler too and will probably just get a 2.5 outlet anyways. So yeah, if you could tell me the stock inlet for the converter you will get all the points I can offer...