First try again, some nifty "traps" in this one. First try because I didn't rush it, but pretty devious, easy to mess up. That was pretty tough for an elementary level, everything you do seems counterintuitive, including the solution. First try! Look ahead and don't rush. I both love and loathe pipelining at the same time. Very well designed elementary level! It may be easy but you still need to think.