What is the missing number?

A woman starts dating a doctor. Before too long, she becomes pregnant and they don't know what to do. About nine months later, just about the time she is going to give birth, a priest goes into the hospital for a prostate gland infection.

The doctor says to the woman: "I know what we'll do. After I've operated on the priest, I'll give the baby to him and tell him it was a miracle."

"Do you think it will work?" she asks.

"It's worth a try," he says.

So, the doctor delivers the baby and then operates on the priest. After the operation he goes in to the priest and says: "Father, you're not going to believe this."

"What happened?" asks the priest.

"You gave birth to a child!"

"But that's impossible!" says the priest.

"I just did the operation," insists the doctor. "It's a miracle! Here's your baby."

About 15 years go by, and the priest realizes he must tell his son the truth. One day, he sits the boy down and says: "Son, I have something to tell you. I'm not your father."

The son says: "What do you mean, you're not my father?"

The priest replies: "I am your mother. The archbishop is your father."