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Given a picture consisting of black and white pixels, and a positive integer N, find the number of black pixels located at some specific row **R** and column **C** that align with all the following rules:

- Row R and column C both contain exactly N black pixels.
- For all rows that have a black pixel at column C, they should be exactly the same as row R

The picture is represented by a 2D char array consisting of 'B' and 'W', which means black and white pixels respectively.

**Example:**

Input:[['W', 'B', 'W', 'B', 'B', 'W'], ['W', 'B', 'W', 'B', 'B', 'W'], ['W', 'B', 'W', 'B', 'B', 'W'], ['W', 'W', 'B', 'W', 'B', 'W']] N = 3Output:6Explanation:All the bold 'B' are the black pixels we need (all 'B's at column 1 and 3). 0 1 2 3 4 5 column index 0 [['W','B', 'W','B', 'B', 'W'], 1 ['W','B', 'W','B', 'B', 'W'], 2 ['W','B', 'W','B', 'B', 'W'], 3 ['W', 'W', 'B', 'W', 'B', 'W']] row index Take 'B' at row R = 0 and column C = 1 as an example: Rule 1, row R = 0 and column C = 1 both have exactly N = 3 black pixels. Rule 2, the rows have black pixel at column C = 1 are row 0, row 1 and row 2. They are exactly the same as row R = 0.

**Note:**

- The range of width and height of the input 2D array is [1,200].

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