Table

Simon 有一个 n × m 的矩形，由（1，1）到（n，m）从左到右从上到下标号。第 x 行第 y 列的位置可以编成 (x，y)，而四个角的坐标是 (1，1);(n，1);(1，m);(n，m)。 Simon 用 1 来标记那些称之为“好”的单元格，并且已知四个角落的单元格都是不好的单元格。不好的单元格用 0 表示。初始，所有单元格都是无色的，Simon 想把所有单元格都染成有色。每一步，他可以先选择任意一个“好”的单元格 (x1，y1)，然后再选任一个角落单元格 (x2，y2)，再把这样两个顶点组成的矩形中的所有单元格都染成某种颜色。 请帮助 Simon 算一下，所有单元格都染成有色，至少需要几步？

Simon has a rectangular table consisting of $ n $ rows and $ m $ columns. Simon numbered the rows of the table from top to bottom starting from one and the columns — from left to right starting from one. We'll represent the cell on the $ x $ -th row and the $ y $ -th column as a pair of numbers $ (x,y) $ . The table corners are cells: $ (1,1) $ , $ (n,1) $ , $ (1,m) $ , $ (n,m) $ . Simon thinks that some cells in this table are good. Besides, it's known that no good cell is the corner of the table. Initially, all cells of the table are colorless. Simon wants to color all cells of his table. In one move, he can choose any good cell of table $ (x_{1},y_{1}) $ , an arbitrary corner of the table $ (x_{2},y_{2}) $ and color all cells of the table $ (p,q) $ , which meet both inequations: $ min(x_{1},x_{2})<=p<=max(x_{1},x_{2}) $ , $ min(y_{1},y_{2})<=q<=max(y_{1},y_{2}) $ . Help Simon! Find the minimum number of operations needed to color all cells of the table. Note that you can color one cell multiple times.

The first line contains exactly two integers $ n $ , $ m $ ( $ 3<=n,m<=50 $ ). Next $ n $ lines contain the description of the table cells. Specifically, the $ i $ -th line contains $ m $ space-separated integers $ a_{i1},a_{i2},...,a_{im} $ . If $ a_{ij} $ equals zero, then cell $ (i,j) $ isn't good. Otherwise $ a_{ij} $ equals one. It is guaranteed that at least one cell is good. It is guaranteed that no good cell is a corner.

Print a single number — the minimum number of operations Simon needs to carry out his idea.

3 3
0 0 0
0 1 0
0 0 0

4

4 3
0 0 0
0 0 1
1 0 0
0 0 0

2

In the first sample, the sequence of operations can be like this: - For the first time you need to choose cell $ (2,2) $ and corner $ (1,1) $ . - For the second time you need to choose cell $ (2,2) $ and corner $ (3,3) $ . - For the third time you need to choose cell $ (2,2) $ and corner $ (3,1) $ . - For the fourth time you need to choose cell $ (2,2) $ and corner $ (1,3) $ . In the second sample the sequence of operations can be like this: - For the first time you need to choose cell $ (3,1) $ and corner $ (4,3) $ . - For the second time you need to choose cell $ (2,3) $ and corner $ (1,1) $ .