<image>(2011 Autumn • Yuecheng District School-Level Midterm) As shown in the figure, the planes of two rectangles ABCD and ABEF are perpendicular to each other. The angles between DE and the plane ABCD and between DE and the plane ABEF are 30° and 45°, respectively. M and N are the midpoints of DE and DB, respectively, and MN = 1. The length of segment AB is ____.