How much of the script was Chaplin + what was Welles?

I read a lot of story about the film which I think is one of Chaplin's best especially his acting. I read that there was a script from Welles that he was going to direct and Chaplin was going to act, of course that didn't happen. So i was just wondering how much of the script was Welles and how much was Chaplin?
On just a personal note I think Charlie Chaplin and Orson Welles where and still are two of the greatest actor/filmmaker in film history.