Let $ABC$ be an isosceles triangle ($AB = AC$), $D$ be the midpoint of $BC$, and $M$ be the midpoint of $AD$. On the segment $BM$ take a point $N$ such that $\angle BND = 90^o$. Find the angle $ANC$.
Problem
Source: 2007 All-Ukrainian Correspondence MO of magazine ''In the World of Mathematics'', grades 5-12 p7
Tags: geometry, isosceles, midpoints, Ukraine Correspondence