Let (x1,y1), (x2,y2), (x3,y3), (x4,y4), and (x5,y5) be the vertices of a regular pentagon centered at (0,0). Compute the product of all positive integers k such that the equality x1k+x2k+x3k+x4k+x5k=y1k+y2k+y3k+y4k+y5k must hold for all possible choices of the pentagon.