  We calculate the polarization operator of the nucleon current in the
instanton medium. The medium (QCD vacuum) is assumed to be a composition of the
instantons of large and small sizes. The former are described in terms of the
local scalar condensate, while the latter can be interpreted as the nonlocal
scalar condensate. We solve the corresponding QCD sum rules equations and
demonstrate that there is a solution with the value of the nucleon mass close
to the physical one if the fraction of the small size instantons w_s \approx
2/3.
