1989 IMO Problems/Problem 5
Let and consider a set of $2n − 1$ (Error compiling LaTeX. ! Package inputenc Error: Unicode char \u8:− not set up for use with LaTeX.) distinct points on a circle. Suppose that exactly of these points are to be colored black. Such a coloring is “good” if there is at least one pair of black points such that the interior of one of the arcs between them contains exactly points from set . Find the smallest value of such that every such coloring of points of is good.