lvl4 starts getting harder since it evaluates both input and output see https://news.ycombinator.com/item?id=35905876 https://news.ycombinator.com/item?id=3590

lvl4 starts getting harder since it evaluates both input and output see https://news.ycombinator.com/item?id=35905876 https://news.ycombinator.com/item?id=35905876 for creative solutions (spoiler alert!)