I need help remembering a joke

I can't remember the punch line. I don't remember much, but here's what I remember:

Little Johnny goes to church ad enters the confessions box. The priest behind the screen says
"Johnny, is that you?"

Johnny- "Yes father, it is me."

Priest- "What sin have you committed, my son?"

Johnny- "I fooled around with a girl"

Priest- "was it Mary?"

Johnny- "I can't say the name, father."

Priest- "was it Rose?"

Johnny- "I can't say the name, father"

Priest- "was it Jane?"

Johnny- "I cat say the name, father."

After this there are a few more lines including a funny punch line, but for the life of me I can't remember what it is. Can someone help me?