[Periodicity and Non-periodicity]

Petya takes black and red cards out of a bag and stacks them in two piles. It is forbidden to place a card on another card of the same color. The tenth and eleventh cards laid out by Petya are 一 red, and the twenty-fifth is black. What color is the twenty-sixth card laid out?

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Note that the positions where two cards of the same color lie on top and the positions where two cards of different colors lie on top alternate. Since the 10th and 11th cards are red, after the 11th card was placed, two cards of the same color (red) were on top. This means that after the 25th card was placed (as well as any card with an odd number), two cards of the same color were on top. Since the 25th card is black, the two top cards are black. Therefore, the next, 26th card can only be red (only a red card can be placed on a black card).

## Answer

Red.