[en] Using a simple optical model with correct normalization, the total hadron-nucleus cross section is expressed in terms of quantities characterizing the hadron-nucleon scattering and of some geometrical factors. On the basis of this expression, calculations are performed and comparison with the experimental data for π+ - A reactions is done at the following energies: 180, 900, 1100, 1350, 1600 MeV. (author)