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())
cost=[[0 for i in range(m)] for i in range(2)]
#one denotes converting to .
#zero denotes converting # 
for i in range(n):
    s=input()
    for i in range(len(s)):
        if(s[i]=='#'):
            cost[1][i]+=1
        else:
            cost[0][i]+=1


fin=[[0 for i in range(m)] for i in range(2)]
pre=[[0 for i in range(m)] for i in range(2)]
for i in range(m):
    if(i==0):
        pre[0][i]=cost[0][i]
        pre[1][i]=cost[1][i]
    else:
        pre[0][i]=pre[0][i-1]+cost[0][i]
        pre[1][i]=pre[1][i-1]+cost[1][i]
for i in range(m):
    if(i==0):
        fin[0][i]=pre[0][i]
        fin[1][i]=pre[1][i]
    else:
        fin[0][i]=fin[1][i-1]+cost[0][i]
        fin[1][i]=fin[0][i-1]+cost[1][i]
        j=i-x
        while(j>0 and j>i-y):
            fin[0][i]=min(fin[1][j-1]+(pre[0][i]-pre[0][j-1]),fin[0][i])
            fin[1][i]=min(fin[0][j-1]+(pre[1][i]-pre[1][j-1]),fin[1][i])
            j-=1
print(min(fin[0][-1],fin[1][-1]))
    
  
            
        
