• Start from S3
• Open and reclose the bottom part in order to push the two tiles of the bottom stack inside the two tiles above. We obtain a flat shape with three stacks, one with four tiles
• Open in half the stack with four tiles about a vertical hinge (rotate 90 degress the two sets of two tiles in opposite directions)
• Lower down two of the four tiles to get locally a flat 2x2 square
• Reclose the square into the final shape