Barcode

2000ms

262144K

Description:

You've got an n × m pixel picture. Each pixel can be white or black. Your task is to change the colors of as few pixels as possible to obtain a barcode picture.

A picture is a barcode if the following conditions are fulfilled:

All pixels in each column are of the same color.
The width of each monochrome vertical line is at least x and at most y pixels. In other words, if we group all neighbouring columns of the pixels with equal color, the size of each group can not be less than x or greater than y.

Input:

The first line contains four space-separated integers n, m, x and y (1 ≤ n, m, x, y ≤ 1000; x ≤ y).

Then follow n lines, describing the original image. Each of these lines contains exactly m characters. Character "." represents a white pixel and "#" represents a black pixel. The picture description doesn't have any other characters besides "." and "#".

Output:

In the first line print the minimum number of pixels to repaint. It is guaranteed that the answer exists.

Sample Input:

6 5 1 2
##.#.
.###.
###..
#...#
.##.#
###..

Sample Output:

Sample Input:

2 5 1 1
#####
.....

Sample Output:

Note:

In the first test sample the picture after changing some colors can looks as follows:


.##..
.##..
.##..
.##..
.##..
.##..

In the second test sample the picture after changing some colors can looks as follows:


.#.#.
.#.#.

Informação

Provedor Codeforces

Código CF225C