Final state interaction in decays B----->Kaon Pion

We discuss the rescattering effects in decays $B\to \pi+K$. The picture we take is very simple: first, B decay into $K*\rho$, then $K*$ and $\rho$ go to kaon and pion by exchanging a pion. We find a up to ten percent CP violation asymmetry rate. We also discuss its correction to the constraint of angle $\gamma$ proposed recently.