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 collections import deque
from itertools import islice

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

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

min_b = [0] + [1001001 for i in range(y-1)]
min_w = [0] + [1001001 for i in range(y-1)]

for i in range(m):
    count_b = 0
    for j in range(n):
        if bars[j][i] == '#':
            count_b += 1

    if x > 1:
        best_b = min(min_b[-y:-x+1])
        best_w = min(min_w[-y:-x+1])
    else:
        best_b = min(min_b[-y:])
        best_w = min(min_w[-y:])

    min_b.append(best_w)
    min_w.append(best_b)
    for j in range(-y, 0):
        min_b[j] += n-count_b
        min_w[j] += count_b
    
if x > 1:
    sol = min(min(min_b[-y:-x+1]), min(min_w[-y:-x+1]))
else:
    sol = min(min(min_b[-y:]), min(min_w[-y:]))

print(sol)
