  Motivated by a classical result of Finn and Osserman (1964), who proved that
the Scherk surface over the square inscribed in the unit disk is extremal for
the Gaussian curvature of the point $O$ (so-called \emph{centre}) of the
minimal graphs above the center $0$ of unit unit disk, provided the tangent
plane is horizontal, we ask and answer to the question concerned the extremal
of "second derivative" of the Gaussian curvature of such graphs provided that
its curvature at $O$ is zero. We prove that the extremals are certain Scherk
type minimal surfaces over the regular hexagon inscribed in the unit disk,
provided that the Gaussian curvature vanishes and the tangent plane is
horizontal at the centre.
