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 "#".
import sys
input = lambda: sys.stdin.readline().rstrip()
from collections import deque,defaultdict,Counter
from itertools import permutations,combinations
from bisect import *
from heapq import *
from math import ceil,gcd,lcm,floor,comb
alph = 'abcdefghijklmnopqrstuvwxyz'
#pow(x,mod-2,mod)

N,M,X,Y = map(int,input().split())
l = [0]*M
for _ in range(N):
    S = input()
    for i in range(M):
        if S[i]=="#":l[i]+=1

dp = [[float('inf')]*(Y+1) for _ in range(M)]
dp[0][0] = l[0]
dp[0][1] = N-l[0]

for i in range(1,M):
    for j in range(X,Y+1):
        dp[i][j] = dp[i-1][j-1]+(N-l[i])

    for j in range(Y+1):
        dp[i][0] = min(dp[i][0],dp[i-1][j]+l[i])

print(min(dp[-1]))
