Hello. When I was in Mathematical Olympiad in our district, I got a example which I can not solve :-( Now, I am very interested in, how to do it. I don't know, my brother - teacher don't know, my friends don't know. I think you can solve it :-) Can you help me? It isn't my homework and I really don't know how to do it easily (don't draw a 63-gon :-D) To each of vertexes of regular 63-gon assign one of the numbers 1 or -1. To each of his sides ascribe the product of numbers of her boundaring vertexes. Then add all numbers at sides. What is the smallest possible non.negative value of this sum? Thank you very much and sorry for my bad English.