Time Limit: 1000 ms
Memory Limit: 65535 ms
Recently WAVWind has finished a great invention named WAVWind pencil!!
Maybe you wonder what aWAVWind pencilis? First of all, the pencil we speak of supports only black and white. Therefore, a picture consists of a rectangular area of pixels, which are either black or white. Second, there is only one operation how to change the colour of pixels:
Select a rectangular area of r rows and c columns of pixels, which is completely inside the picture. As a result of the operation, each pixel inside the selected rectangle changes its colour (from black to white, or from white to black).
Initially, all pixels are white. To create a picture, the operation described above can be applied several times. Can you paint a certain picture which you have in mind?