China Mathematics Olympiads (National Round) 2008 Problem 5
Source:
November 28, 2010
geometrytrapezoidpigeonhole principlecombinatorics
Problem Statement
Find the smallest integer satisfying the following condition: regardless of how one colour the vertices of a regular -gon with either red, yellow or blue, one can always find an isosceles trapezoid whose vertices are of the same colour.