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;input = sys.stdin.readline
inf = int(1e10)
n, m, x, y = map(int, input().split())
matrix = [list(input().strip()) for _ in range(n)]
b, w = [0]*m, [0]*m
for j in range(m):
	for i in range(n):
		if matrix[i][j] == '#': b[j] += 1
		else: w[j] += 1
dp = [[inf, inf] for i in range(m)]
dp[0][0], dp[0][1] = w[0], b[0]
for i in range(1, m):
	l, r = max(0, i-y+1), max(0, i-x+1)
	for j in range(l, r+1):
		dp[i][0] = min(dp[i][0], sum(w[j:i+1])+dp[j-1][1])
		dp[i][1] = min(dp[i][1], sum(b[j:i+1])+dp[j-1][0])
print(min(dp[-1]))