If \(f(x)=\frac{ax+b}{cx+d}, abcd\not=0\) and \(f(f(x))=x\) for all \(x\) in the domain of \(f\), what is the value of \(a+d\)?
As seen by the example f(x) = (x + 1)/(-x + 1), a + d = 2.
+343 
