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())
a = [input() for _ in range(n)]
b_cols = [0] * m
w_cols = [0] * m
for i in range(n):
    for j in range(m):
        if a[i][j] == '#':
            b_cols[j] += 1
        else:
            w_cols[j] += 1
INF = 1000000000
dp = [[[INF] * (m + 1) for __ in range(y + 1)] for _ in range(2)]
dp[0][0][0] = 0
dp[1][0][0] = 0
for i in range(1, m + 1):
    for len in range(x, y + 1):
        dp[0][0][i] = min(dp[0][0][i], dp[1][len][i - 1] + b_cols[i - 1])
        dp[1][0][i] = min(dp[1][0][i], dp[0][len][i - 1] + w_cols[i - 1])
    for len in range(1, y + 1):
        dp[0][len][i] = min(dp[0][len][i], dp[0][len - 1][i - 1] + b_cols[i - 1])
        dp[1][len][i] = min(dp[1][len][i], dp[1][len - 1][i - 1] + w_cols[i - 1])

ans = INF
for len in range(x, y + 1):
    ans = min(ans, dp[0][len][m], dp[1][len][m])

print(ans)
