说明：  Ural 1221 Malevich Strikes Back代码，简洁明了，通过搜索正方中心坐标并判定来实现
( After the greatest success of Malevich s Black Square the famous artist decided to create a new masterpiece. He took a large sheet of checked paper and filled some cells with black. After that he realized the picture to be too complicated. He was afraid, that people would not understand the sense of the painting. Thus, Malevich decided to cut out a smaller picture of the special form. It should be a black square with its sides parallel to the sides of the list. A white square rotated by 45 degrees should be placed inside the black square. The corners of the white square should lay on the sides of the black square. You can see an example of such picture on the figure. The original paper size is N × N, 0 < N ≤ 100. Your program should help Malevich to find the largest figure corresponding to the pattern described above. The input contains several test cases. Each test case starts with the size of paper N. The following N lines of the test case describe the original painting: 1 )