IMO Shortlist 2011 problem C2
Dodao/la: arhiva23. lipnja 2013.
students are standing in a circle. Prove that there exists an integer
such that in this circle there exists a contiguous group of
students, for which the first half contains the same number of girls as the second half.
Proposed by Gerhard Wöginger, Austria
Izvor: Međunarodna matematička olimpijada, shortlist 2011