  Consider two normal leads coupled to a superconductor; the first lead is
biased while the second one and the superconductor are grounded. In general, a
finite current $I_2(V_1,0)$ is induced in the grounded lead 2; its magnitude
depends on the competition between processes of Andreev and normal
quasiparticle transmission from the lead 1 to the lead 2. It is known that in
the tunneling limit, when normal leads are weakly coupled to the
superconductor, $I_2(V_1,0)=0$, if $|V_1|<\Delta$ and the system is in the
clean limit. In other words, Andreev and normal tunneling processes compensate
each-other. We consider the general case: the voltages are below the gap, the
system is either dirty or clean. It is shown that $I_2(V_1,0)=0$ for general
configuration of the normal leads; if the first lead injects spin polarized
current then $I_2=0$, but spin current in the lead-2 is finite. XISIN
structure, where X is a source of the spin polarized current could be applied
as a filter separating spin current from charge current. We do an analytical
progress calculating $I_1(V_1,V_2), I_2(V_1,V_2)$.
