You need to sort the numbers from 1 to 15 in ascending order. For a valid decision, an empty cell can only be located either at the beginning of the field or at the end. See help for possible solutions. If you're stuck and can't come up with a solution, try to solve the puzzle on the right side. They say that any mixed configuration can be converted to the initial one in no more than 80 moves. And how much will you need?
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