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 "#".
import sys
input = sys.stdin.readline


n, m, x, y = map(int, input().split())
g = [input()[:-1] for _ in range(n)]
w = [sum([1 if g[i][j] == '#' else 0 for i in range(n)]) for j in range(m)]
M = [10**9]*(2*y)
d = [[0]*(2*y)]
for i in range(m):
    d.append(M.copy())
    a, b = w[i], n-w[i]
    for j in range(2*y):
        if j < y-1:
            d[-1][j+1] = min(d[-2][j]+a, d[-1][j+1])
        elif y <= j < 2*y-1:
            d[-1][j+1] = min(d[-2][j]+b, d[-1][j+1])
        if x-1 <= j < y:
            d[-1][y] = min(d[-2][j]+b, d[-1][y])
        elif y+x-1 <= j:
            d[-1][0] = min(d[-2][j]+a, d[-1][0])
print(min(d[-1]))
