A 5 × 5 square is made from 1 × 1 tiles, all with the same pattern, as shown. Any two adjacent tiles have the same colour along the shared edge. The perimeter of the 5 × 5 square consists of black and white segments of length 1. What is the smallest possible number of black segments on the perimeter of the 5 × 5 square?
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Grey Kangaroo 2014 (2014)
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