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 "#".
INF = 2147483647

n, m, x, y = list(map(int, input().split()))
barcode = []
for _ in range(n):
    barcode.append(list(input()))
column_black = [-1] * m
column_white = [-1] * m

def column(x, colour):
    re = 0
    for i in range(n):
        if barcode[i][x] != colour:
            re += 1
    return re

for i in range(m):
    column_black[i] = column(i, '#')
    column_white[i] = column(i, '.')

def solve(index, is_black, consec):
    if index == 0:
        return 0
    index -= 1
    change_black = INF
    change_white = INF
    if is_black and consec < x:
        change_black = solve(index, True, consec + 1)
    elif is_black and consec >= y:
        change_white = solve(index, False, 1)
    elif not is_black and consec < x:
        change_white = solve(index, True, consec + 1)
    elif not is_black and consec >= y:
        change_black = solve(index, True, 1)
    else:
        if is_black:
            change_black = solve(index, True, consec + 1)
            change_white = solve(index, False, 1)
        else:
            change_white = solve(index, False, consec + 1)
            change_black = solve(index, True, 1)
    change_white += column_white[index]
    change_black += column_black[index]
    return min(change_white, change_black)

print(min(solve(m, True, 1), solve(m, False, 1)))
