Gardon asked me to produce a problem for his own contest a weed ago, which contest celebrate for his remove. I make the problem that can be solved by a dynamic programming, which is my favorite recently, and used half a hour to write the standard code and the program to generate data. But when I asked flymouse to check the data he said that I make the problem hard to understand, I explained a minutes then decide to give up, replaced to rewrite the problem by English, maybe English is more understandable.