5.3.2.24 Various problems in the space

condition: At the base of the pyramid \( S A B C D \) there is a square with side \( a \), and the side edge \( S B \) is perpendicular to the plane of the base and equal to the side of the base. On the edges \( S D \) and \( A D \) the points \( M \) and \( L \) are taken, respectively, - the midpoints of these edges. Find the distance between the lines \( M L \) and \( A C \).