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输入样例：3
输出样例：
step 1:move 1 from A to C
step 2:move 2 from A to B
step 3:move 1 from C to B
step 4:move 3 from A to C
step 5:move 1 from B to A
step 6:move 2 from B to C
step 7:move 1 from A to C