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 "#".
from math import inf
n,m,x,y = map(int, input().split())
A = []
for _ in range(n):
    A.append(input())

pref = [(0,0)]
for j in range(m):
    hashtags = sum(1 if A[i][j] == "#" else 0 for i in range(n))
    pref.append(
            (pref[-1][0] + hashtags, # white
            pref[-1][1] + n - hashtags) # black
            ) 

dp = [[inf] * 2 for _ in range(m+1)]
dp[0] = [0,0]

for j in range(1,m+1):
    for c in range(2):
        for w in range(x,y+1):
            if j-w < 0:
                break
            dp[j][c] = min(dp[j][c], dp[j-w][1-c] + pref[j][c] - pref[j-w][c])

print(min(dp[-1]))
