IMO Shortlist 2012 problem C7


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3. studenoga 2013.
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There are given 2^{500} points on a circle labeled 1,2,\ldots ,2^{500} in some order. Prove that one can choose 100 pairwise disjoint chords joining some of theses points so that the 100 sums of the pairs of numbers at the endpoints of the chosen chord are equal.
Izvor: Međunarodna matematička olimpijada, shortlist 2012