CF323A.Black-and-White Cube

You are given a cube of size k × k × k, which consists of unit cubes. Two unit cubes are considered neighbouring, if they have common face.

Your task is to paint each of _k_3 unit cubes one of two colours (black or white), so that the following conditions must be satisfied:

• each white cube has exactly 2 neighbouring cubes of white color;
• each black cube has exactly 2 neighbouring cubes of black color.

给你一个大小为 $k \times k \times k$ 的立方体，它由单位立方体组成。若两个单位立方体具有公共面，则称它们为相邻。

你的任务是将全部 $k^3$ 个单位立方体各自涂成两种颜色之一（黑色或白色），使得满足以下条件：

• 每个白色单位立方体恰好有 2 个白色邻居；
• 每个黑色单位立方体恰好有 2 个黑色邻居。

The first line contains integer k (1 ≤ k ≤ 100), which is size of the cube.

第一行包含一个整数 $k$（$1 \leq k \leq 100$），表示立方体的大小。

Print -1 if there is no solution. Otherwise, print the required painting of the cube consequently by layers. Print a k × k matrix in the first k lines, showing how the first layer of the cube should be painted. In the following k lines print a k × k matrix — the way the second layer should be painted. And so on to the last k-th layer. Note that orientation of the cube in the space does not matter.

Mark a white unit cube with symbol "w" and a black one with "b". Use the format of output data, given in the test samples. You may print extra empty lines, they will be ignored.

如果无解，输出 -1。否则，按层次顺序输出立方体的染色方案：前 $k$ 行输出一个 $k \times k$ 的矩阵，表示立方体第一层的染色方式；接下来的 $k$ 行再输出一个 $k \times k$ 的矩阵，表示第二层的染色方式；依此类推，直至第 $k$ 层。注意：立方体在空间中的朝向无关紧要。

用字符 "w" 表示白色小立方体，"b" 表示黑色小立方体。输出格式需与样例测试数据一致。允许输出额外的空行，它们将被忽略。