  An algebra with identities $a\circ(b\circ c-c\circ b)=(a\circ b)\circ
c-(a\circ c)\circ b$ and $a\circ(b\circ c)=b\circ(a\circ c)$ is called Novikov.
We construct free Novikov base in terms of Young diagrams. We show that
codimensions exponent for a variety of Novikov algebras exists and is equal 4.
