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 = [0]*(m+1)
for i in range(n):
    q = input()[:-1]
    for j in range(m):
        if q[j] == '#':
            a[j+1] += 1
b = [n-i for i in a]
q = [[1001 for i in range(y)] for j in range(m+1)]
w = [[1001 for i in range(y)] for j in range(m+1)]
for i in range(1, m+1):
    for j in range(y):
        if j == 0:
            a1, b1 = min(w[i-1][x-1:]), min(q[i-1][x-1:])
            q[i][j], w[i][j] = a1 + a[i] if a1 != 1001 else a[i], b1 + b[i] if b1 != 1001 else b[i]
        else:
            if q[i-1][j-1] != 1001:
                q[i][j], w[i][j] = q[i-1][j-1] + a[i], w[i-1][j-1] + b[i]

print(min(min(q[-1][x-1:], w[-1][x-1:])))
