78 year old couple seek Sex Therapist

A couple, both age 78, went to a sex therapist's office. The doctor asked, "What can I do for you?"
The man said, "Will you watch us have sex?"
The doctor looked puzzled but agreed.
When the couple finished, the doctor said, "There's nothing wrong with the way you have sex," and charged them $50.
This happened several weeks in a row. The couple would make an appointment, have sex with no problems, pay the doctor, then leave.
Finally, the doctor asked, "Just exactly what are you trying to find out?"
"We're not trying to find out anything," the husband replied.
"She's married and we can't go to her house. I'm married and we can't go to my house. The Holiday Inn charges $90. The Hilton charges $108. We do it here for $50...and I get $43 back from Medicare.