Modelling the orbital period (top panel), Roche lobe filling factor (middle panel) and radius of the red giant main component (lower panel) of binary system with MESA with the approximated values of KIC 5006817. The models start at the zero age main sequence (ZAMS) and stop with the onset of the RLOF. The dashed line marks the end of the hydrogen core burning (TAMS). The solid line marks the bottom of the RGB. The position of a model with the radius of 6 R_⊙, which equals the current state of KIC 5006817 is shown as a red dot.