<image>(2012 Autumn•Yingjiang District School Final) As shown in the figure, in parallelogram ABCD, \(2|AB|^2 + |BD|^2 - 4 = 0\), \(\angle ABD = 90^\circ\). Fold along BD to form a right dihedral angle A-BD-C, then the length of the diagonal AC of the spatial quadrilateral ABCD is ____.