  We search for decays of the type B0(Bs)->h+h'- (where h,h'= K or pi) in 180
pb-1 of p-pbar collisions collected at the Tevatron by the upgraded Collider
Detector at Fermilab. We report the first observation of the new mode Bs->K+K-
with a yield of 236 +- 32 events, corresponding to
(f_s/f_d)*BR(Bs->K+K-)/BR(B0->K+pi-) = 0.46+-0.08(stat.)+-0.07(syst.), where
f_s/f_d is the ratio of production fractions of Bs and B0. We find results in
agreement with world averages for the B0 modes, and set the following new
limits at 90% CL: BR(Bs->K-pi+) < 5.6*10^{-6} and BR(Bs->pi+pi-) < 1.7*10^{-6}.
