  We find exact solution in the Cahn eikonal model, which describes
Coulomb-nuclear interference in elastic scattering of charged hadrons. The
cases of both point-like and extended particles equipped with electromagnetic
form factors are considered. According to the solution obtained the
Coulomb-nuclear contributions are not exponentiated and cannot be added to the
Coulomb phase. At the same time, the $O(\alpha)$-approximation of the amplitude
is ambiguous, which makes it unsuitable for data processing.
