f(3)=1/f(1)=-1/5.
f(5)=1/f(3)=-5
f(x)=1/f(x+2)
f(f(5))=f(-5)=1/f(-3)=1/(1/f(-1))=f(-1)=1/f(1)=1/(1/f(3))=f(3)=-5