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1998 hexagons, 666 don't share a vertex (Ukraine 1998 Grade 8 P2)

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June 3, 2021
combinatoricsgeometrycombinatorial geometry

Problem Statement

The plane is partitioned into congruent regular hexagons. Of these hexagons, some 19981998 are marked. Show that one can select 666666 of the marked hexagons in such a way that no two of them share a vertex.