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.

The first line contains integer $ k $ $ (1

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.