The expression of the absorptive part of the nucleon-nucleon scattering amplitude in the "strip approximation" is given. Utilizing the experimental data of low energy π-N scattering, the total cross section of N-N inelastic scattering at 4 BeV. laboratory energy is calculated. For p-p scattering we find σin=25 mb., in agreement with the experimental data. However, the isotopic spin dependence is important in the energy region 3-4 BeV. The result shows that the internal part of the spectral function may be also important.