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())
d={'#':0,'.':1}
l=[[0,0] for i in range(m)]
for i in range(n):
	s=input()
	for j in range(m):
		l[j][d[s[j]]]+=1
pb,pw=[0],[0]
for i in range(m):
	pb.append(pb[-1]+l[i][0])
	pw.append(pw[-1]+l[i][1])
dp=[[float('inf')]*(m+1) for i in range(2)]
dp[0][0]=dp[1][0]=0
for i in range(1,m+1):
	for j in range(x,y+1):
		if i-j>=0:
			dp[0][i]=min(dp[0][i],dp[1][i-j]+pb[i]-pb[i-j])
			dp[1][i]=min(dp[1][i],dp[0][i-j]+pw[i]-pw[i-j])
print(min(dp[0][-1],dp[1][-1]))
    