  We present photometric observations in Sloan filters g', i' of the eclipsing
W UMa stars USNO-A2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The
sinusoidal-like O-C diagram of V471 Cas shows presence of third body with mass
of 0.12 Msun (red dwarf) at distance 897 Rsun. The O-C diagram of V479 Lac
reveals period decreasing. The results of the light curve solutions are: (i)
The targets are overcontact binaries with small fill-out factors; (ii) Their
components are F-K stars, comparable in size, whose temperature differences are
below 80 K; (iii) All targets undergo partial eclipses and to limit the
possible mass ratios we carried out two-step $q$-search analysis. The target
global parameters (luminosities, radii, masses) were obtained on the base of
their GAIA distances and the results of our light curve solutions. The obtained
total mass of V560 Lac turns out smaller than the lower mass limit for the
presently existing W UMa binaries of 1.0-1.2 Msun, i.e. this target is an
peculiar overcontact system.
