The problem this time is to get the median of three values (easy)

I did this:

(define (med x y z) (car(cdr(x y z)))

and it was accepted but when testing it:

(med 3 4 5)

I get this error:

Error: attempt to call a non-procedure
(2 3 4)

And when entering letters instead of number i get:

(md x y z)

Error: undefined varia
y
(package user)

Using something besides x y z I get:

(md d l m)

Error: undefined variable
d
(package user)

the question was deleted dont know how anyway

write a function that return the median of 3 values