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*.
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 "#".
from sys import stdin, stdout




def main():
    n, m, x, y = map(int, stdin.readline().split())
    
    b_pixels = [0]*(m+1)
    w_pixels = [0]*(m+1)
    
    for _ in range(n):
        l = stdin.readline().strip()
        for i in range(len(l)):
            if l[i] == "#":
                b_pixels[i+1] += 1
            else:
                w_pixels[i+1] += 1
    
    for i in range(1, m+1):
        b_pixels[i] += b_pixels[i-1]
        w_pixels[i] += w_pixels[i-1]
    
    dpw = [1e9] * (m+1)
    dpb = [1e9] * (m+1)
    # min pixels to paint given that ith one is white
    def w(k):
        if k < 0 :
            return 1e9
        if k == 0:
            return 0
        if dpw[k] != 1e9:
            return dpw[k]
        
        cost = 1e9
        for j in range(x, y+1):
            if k-j < 0:
                break
            paint_white_pixels = w_pixels[k] - w_pixels[k-j]
            paint_rest = b(k-j)
            cost = min(cost, paint_white_pixels + paint_rest)
        
        dpw[k] = cost
        return cost
    def b(k):
        if k < 0 :
            return 1e9
        if k == 0:
            return 0
        if dpb[k] != 1e9:
            return dpb[k]
        
        cost = 1e9
        for j in range(x, y+1):
            if k-j < 0:
                break
            paint_black_pixels = b_pixels[k] - b_pixels[k-j]
            paint_rest = w(k-j)
            cost = min(cost, paint_black_pixels + paint_rest)
        
        dpb[k] = cost
        return cost
    
    print(min(w(m), b(m)))
            
        
        
        
    
main()
