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 = sys.stdin.readline
def multi_input():
    return map(int, input().split())

def array_print(arr):
    print(' '.join(map(str, arr)))


def same_rows(matrix, n,m):
    repaint = [[0 for i in range(m)] for j in range(2)]
    for i in range(m):
        for j in range(n):
            if matrix[j][i] == '.':
                repaint[0][i] += 1
            else:
                repaint[1][i] += 1
        repaint[0][i] += repaint[0][i-1]
        repaint[1][i] += repaint[1][i-1]
    return repaint


def solve(repaint, dp, type, index, x,y):
    if dp[type][index] == -1:
        dp[type][index] = 100000000

        for i in range(x, y+1):
            if index-i>0:
                temp = solve(repaint, dp, 1 - type, index-i, x,y) + repaint[type][index] - repaint[type][index-i]
            else: temp =  solve(repaint, dp, 1 - type, index-i, x,y) + repaint[type][index]
            dp[type][index] = min(dp[type][index], temp)

    return dp[type][index]

n, m, x, y = multi_input()
matrix = []
for i in range(n):
    s = input()
    matrix.append(s)
repaint = same_rows(matrix,n,m)
# print(repaint)
dp = [[-1 for i in range(m)] for j in range(2)]
dp[0][0] = 0
dp[1][0] = 0

print(min(solve(repaint, dp, 0, m-1, x,y), solve(repaint, dp, 1, m-1, x,y)))
