Starting state: there are 4 stacks: - Stack 1: green block (alone) - Stack 2: blue block (alone) - Stack 3: purple block (alone) - Stack 4: red block, yellow block, from bottom to top Ending state: there are 5 stacks: - Stack 1: yellow block (alone) - Stack 2: red block (alone) - Stack 3: purple block (alone) - Stack 4: blue block (alone) - Stack 5: green block (alone)