  As was firstly shown by E. Bogomolny, the critical Ginzburg-Landay (GL)
parameter kappa =1/sqrt{2} at which a superconductor changes its behavior from
type-I to type-II, is the special highly degenerate point where Abrikosov
vortices do not interact and therefore all vortex states have the same energy.
Developing a secular perturbation theory we studied how this degeneracy is
lifted when kappa is slightly different from 1\sqrt{2} or when the GL theory is
extended to the higher in T-Tc terms. We constructed a simple secular
functional, that depends only on few experimentally measurable phenomenological
parameters and therefore is quite efficient to study the vortex state of
superconductor in this transitional region of kappa. Basing on this, we
calculated such vortex state properties as: critical fields, energy of the
normal-superconductor interface, energy of the vortex lattice, vortex
interaction energy etc. and compared them with previous results that were based
on bulky solutions of GL equations.
