  Under assumption of singular behavior of alpha_s(q^2) at q^2 sim 0 and of
large q^2 behavior, corresponding to the perturbation theory up to four loops,
a procedure is considered of matching the beta-function at a boundary of
perturbative and non-perturbative regions. The contribution of the
non-perturbative region to the gluon condensate is calculated with varying
normalization condition alpha_s(m_tau^2) = 0.29, 0.30,..., 0.36 for two
different ways of definition of the non-perturbative invariant charge in the
infrared region. We obtain quite consistent results for values of the gluon
condensate, nonperturbative region scale q_0, and the string tension sigma.
