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, '.')

black = [[INF] * (y + 1) for _ in range(m + 1)]
white = [[INF] * (y + 1) for _ in range(m + 1)]
for i in range(x, y + 1):
    black[0][i] = 0
    white[0][i] = 0

# black
for index in range(1, m + 1):
    for consec in range(y + 1):
        change_black = INF
        change_white = INF
        if consec < x:
            change_black = black[index - 1][consec + 1]
        elif consec >= y:
            change_white = white[index - 1][1]
        else:
            change_black = black[index - 1][consec + 1]
            change_white = white[index - 1][1]
        change_white += column_white[index - 1]
        change_black += column_black[index - 1]
        black[index][consec] = min(change_black, change_white)
        # white
        change_black = INF
        change_white = INF
        if consec < x:
            change_white = white[index - 1][consec + 1]
        elif consec >= y:
            change_black = black[index - 1][1]
        else:
            change_black = black[index - 1][1]
            change_white = white[index - 1][consec + 1]
        change_white += column_white[index - 1]
        change_black += column_black[index - 1]
        white[index][consec] = min(change_black, change_white)


# for row in black: print(row)
# print('')
# for row in white: print(row)

print(min(black[m][0], white[m][0]))