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 "#".
n, m, x, y = map(int, input().split())

M = []
for i in range(n):
    M.append(list(input()))

whites = [0] * m
blacks = [0] * m

for j in range(m):
    for i in range(n):
        whites[j] += 1 if M[i][j] == '.' else 0
        blacks[j] += 1 if M[i][j] == '#' else 0

white_stripes = [[0 for w in range(y + 1)] for j in range(m)]
black_stripes = [[0 for w in range(y + 1)] for j in range(m)]

for j in range(m):
    for w in range(1, y + 1):
        if j + w - 1 >= m:
            break
        white_stripes[j][w] = white_stripes[j][w - 1] + blacks[j + w - 1]
        black_stripes[j][w] = black_stripes[j][w - 1] + whites[j + w - 1]

dp = [[-1, -1] for i in range(m + 1)]


def find_min(column, color):
    if column == m:
        return 0
    if dp[column][color] != -1:
        return dp[column][color]
    res = 10 ** 6 + 1
    stripes = white_stripes if color == 1 else black_stripes
    for w in range(x, y + 1):
        if column + w > m:
            break
        # print('column', column, 'color', color, 'width', w)
        r = stripes[column][w] + find_min(column + w, (0 if color == 1 else 1))
        res = min(res, r)
        # print('column', column, 'color', color, 'width', w, 'res', r)

    dp[column][color] = res
    return res


ans = min(find_min(0, 0), find_min(0, 1))
print(ans)
