Left-hand side: cumulative distribution of the apparent magnitude in the i band for the LSST simulation compared to the Sloan Digital Sky Survey (SDSS) measurement from the Stripe 82 region (cf. Abazajian et al. 2009). The statistical error bars from the data are smaller than the dots size. Right-hand side: redshift distribution of galaxies for the LSST: i < 24, i < 25 with σ_i < 0.2 (solid red, solid black curves respectively); i < 27 with S  ! N > 5 in at least the i band for one and ten years of observations (dotted and solid magenta respectively); S  ! N > 5 in all bands for one and ten years of observations (dotted and solid blue respectively).