Parse path model builder

[MaryamRashidfar]

Hello, I want to know how can I delete the first part of file name in model builder. I used parse path to parse the name for all feature class in my gdb. For example, one of the my file name is DEM31K06NE, so I want that my result be like T31K06NE_p. All my files are the same way, and I want juste delete 3 first letter (DEM) and replace it with T. Which expression can I use? Thanks