  We prove the additive version of the conjecture proposed by Ginzburg and
Kaledin. This conjecture states that if X/G is an orbifold modeled on a
quotient of a smooth affine symplectic variety X (over C) by a finite group
G\subset Aut(X) and A is a G-stable quantum algebra of functions on X then the
graded vector space HH(A^G) of the Hochschild cohomology of the algebra A^G of
invariants is isomorphic to the graded vector space H_{CR}(X/G)((h)) of the
Chen-Ruan (stringy) cohomology of the orbifold X/G.
