On one equality of integrals

The note proves the equality
$$\frac1{2\pi i}\mskip-8mu\oint_{|z|=r}\mskip-8mu\ln\mskip-4mu\left[1{-}f(z)\left(z{+}\frac1z\right)\right]dz= -\frac1{2\pi i}\mskip-8mu\oint_{|z|=r}\mskip-4mu\exp\left(\frac{1{-}\sqrt{1-4f^2(z)}}{2zf(z)}\right)dz.$$