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 "#".
# from debug import debug
import sys
inf = int(1e7)

n, m, x, y = map(int, input().split())
matrix = [list(input()) for i in range(n)]

cw = [0]*(m+1)
cb = [0]*(m+1)

prev1 = 0
prev2 = 0
for i in range(m):
	v = 0
	for j in range(n):
		if matrix[j][i] == '#':
			v+=1
	cb[i+1] = prev1+v
	cw[i+1] = n-v+prev2
	prev1 = cb[i+1]
	prev2 = cw[i+1]

# debug(cb=cb, cw=cw)
dp = [[0 for i in range(m+1)] for i in range(2)]

for i in range(m+1):
	b, w = inf, inf
	for a in range(i-y, i-x+1):
		a = max(0, a)
		b = min(b, dp[0][a]+(cb[i]-cb[a]))
		w = min(w, dp[1][a]+(cw[i]-cw[a]))
	dp[1][i] = b
	dp[0][i] = w

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

