Evil warlock doesn't like dwarfs so he chooses four of them and buries them into the ground so that only their heads are above surface. Dwarfs can't move at all and they can look only forward.

They're buried in a line and one of them is separated by a wall. They are all facing the same direction: last dwarf sees two heads of his friends and a wall. Second last sees only one had and a wall. Second dwarf sees only the wall and first is looking to the distance where he can see nothing interesting though.

Warlock explains the situation to dwarfs and tells them that he has placed hats on their heads - two blue hats and two red ones. One of the dwarfs is supposed to say what color is the hat he is wearing. If he says the right color warlock will dig them out immediately. If he says something else all of them will stay there till the end...

How will dwarfs solve this problem?

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