The (Q) over bar equations, rooted in the dual superconformal anomalies, are a powerful tool for computing amplitudes in planar N = 4 supersymmetric Yang-Mills theory. By using the (Q ) over bar equations, we compute the symbol of the first MHV amplitude with algebraic letters the three-loop 8-point amplitude (or the octagon remainder function) in this theory. The symbol alphabet for this amplitude consists of 204 independent rational letters and shares the same 18 algebraic letters with the two-loop 8-point NMHV amplitude.