# Light

### 题目描述

Teacher Mai has a board of n rows and m columns. There is a light in each cell.
He can flip some lights: if this light is on, turn it off, else turn it on.
He can choose a cell(i,j), and he has following two operations:
1. Flip the light on the cells which share a common edge with cell(i,j).
2. Flip the light on the cells which share a common edge with cell(i,j) and cell(i,j).

You are given the initial state of board. Output the minimum operations to turn off the all the lights.

### 输入格式

There are multiple test cases, terminated by a line "0 0".
For each test case, the first line contains two integers n,m(1<=n,m<=10).
In following n lines, each line contains a string consisting of m characters, representing the initial state(0 means off, 1 means on).

### 输出格式

For each case, output "Case #k: ans" first, where k is the case number counting from 1, ans is the minimum operations.

```3 3
111
111
111
3 3
000
010
000
0 0```

### 样例输出

```Case #1: 3
Case #2: 2
```

By 镇海中学