  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.
