We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey ( ASAS ) catalogue . We measure absolute physical and orbital parameters for this system based on archival V -band and I -band ASAS photometry , as well as on high-resolution spectroscopic data obtained with ESO 3.6m/HARPS and CORALIE spectrographs . The physical and orbital parameters of the system were derived with an accuracy of about 0.5 – 3 % . The system is a very rare configuration of two bright well-detached giants of spectral types K1 and K4 and luminosity class II . The radii of the stars are R _ { 1 } = 52.12 \pm 1.38 and R _ { 2 } = 67.63 \pm 1.40 R _ { \odot } and their masses are M _ { 1 } = 4.914 \pm 0.021 and M _ { 2 } = 4.875 \pm 0.021 M _ { \odot } . The exquisite accuracy of 0.5 % obtained for the masses of the components is one of the best mass determinations for giants . We derived a precise distance to the system of 2.14 \pm 0.06 kpc ( stat . ) \pm 0.05 ( syst . ) which places the star in the Sagittarius-Carina arm . The Galactic rotational velocity of the star is \Theta _ { s } = 258 \pm 26 km s ^ { -1 } assuming \Theta _ { 0 } = 238 km s ^ { -1 } . A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years . The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code .