Let `z_1, z_2,z_3` be complex numbers (not all real) such that `|z_1|=|z_2|=|z_3|=1 and 2(z_1+z_2+z_3)-3z_1 z_2 z_3` is real. Then, `Max (arg(z_1), arg(z_2), arg(z_3))` (Given that argument of `z_1, z_2, z_3` is possitive ) has minimum value as `(kpi)/6` where `(k+2)` is