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())
s = [input() for _ in range(n)]
dp = [[[1e18, 1e18] for i in range(y+1)] for j in range(m)]
ct = [0 for i in range(m)]

for i in range(n):
	for j in range(m):
		if(s[i][j] == '.'): 
			ct[j] += 1

dp[0][1][1] = ct[0]
dp[0][1][0] = n - ct[0]
for i in range(1, m):
	for j in range(1, y+1):
		dp[i][j][1] = dp[i-1][j-1][1] + ct[i]
		dp[i][j][0] = dp[i-1][j-1][0] + n - ct[i]
		if j >= x:
			dp[i][1][0] = min(dp[i][1][0], dp[i-1][j][1] + n - ct[i])
			dp[i][1][1] = min(dp[i][1][1], dp[i-1][j][0] + ct[i])

res = 1e18
for i in range(x, y+1):
	res = min(res, min(dp[-1][i]))
print(res)
