CF717E Paint it really, really dark gray

给你一棵节点编号为$1...n$的树，每个节点都有两种颜色：粉色或黑色。现在你要从1号节点（即树根）出发，每经过一个节点，该节点的颜色就会改变。（粉色变为黑色，黑色变为粉色）。 现在请你找出一条从1号节点（即树根）出发的路径，使得沿这条路径走完后，所有的节点颜色都变为黑色。**注意：你可以经过一个节点或一条边多次，并且路径不要求一定要在1号节点（即树根）结束。** -----------------------------

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At the beginning squirrel is at node 1 and its color is black. Next steps are as follows: - From node $ 1 $ we walk to node $ 4 $ and change its color to pink. - From node $ 4 $ we walk to node $ 2 $ and change its color to pink. - From node $ 2 $ we walk to node $ 5 $ and change its color to black. - From node $ 5 $ we return to node $ 2 $ and change its color to black. - From node $ 2 $ we walk to node $ 4 $ and change its color to black. - We visit node $ 3 $ and change its color to black. - We visit node $ 4 $ and change its color to pink. - We visit node $ 1 $ and change its color to pink. - We visit node $ 4 $ and change its color to black. - We visit node $ 1 $ and change its color to black.