  We perform a combined analysis of antikaon-nucleon scattering cross sections
and the recent SIDDHARTA kaonic hydrogen data in the framework of a
coupled-channel Bethe-Salpeter approach at next-to-leading order in the chiral
expansion of the effective potential. We find a precise description of the
antikaon-proton scattering amplitudes and are able to extract accurate values
of the scattering lengths, a0=-1.81^+0.30_-0.28 + i 0.92^+0.29_-0.23 fm,
a1=+0.48^+0.12_-0.11 + i 0.87^+0.26_-0.20 fm. We also discuss the two-pole
structure of the Lambda(1405).
