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(' '))

arr = []
for i in range(n):
    dummy = list(input())
    arr.append(dummy)

cntW = []
for i in range(m):
    blanks = 0
    for j in range(n):
        if(arr[j][i] == '.'):
            blanks += 1
    cntW.append(blanks)

cntB = []
for i in range(m):
    blanks = 0
    for j in range(n):
        if(arr[j][i] == '#'):
            blanks += 1
    cntB.append(blanks)

prefixW = [0]
prefixB = [0]

curr = 0
for i in range(m):
    curr += cntW[i]
    prefixW.append(curr)

curr = 0
for i in range(m):
    curr += cntB[i]
    prefixB.append(curr)

dp = []
MAX = 1000000
for i in range(m):
    dp.append([MAX]*2)

# 1 color white 0 color black
dp[0][1] = prefixW[1]
dp[0][0] = prefixB[1]

for i in range(1,m):
    # print(i,x,y)
    for k in range(max(0,i-y), max(0,i-x+1)):
        dp[i][1] = min(dp[i][0],dp[k][0] + prefixW[i+1]-prefixW[k+1])
        dp[i][0] = min(dp[i][1],dp[k][1] + prefixB[i+1]-prefixB[k+1])

# print(dp)
print(min(dp[m-1][0], dp[m-1][1]))



