OBM 2015 Problem 1

Let $\triangle ABC$ be an acute-scalene triangle, and let $N$ be the center of the circle wich pass trough the feet of altitudes. Let $D$ be the intersection of tangents to the circumcircle of $\triangle ABC$ at $B$ and $C$ . Prove that $A$ , $D$ and $N$ are collinear iff $\measuredangle BAC = 45º$ .