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 "#".
dp = {}
h, w, x, y = 0, 0, 0, 0
a = [0] * 1000
white, black = 0, 1
def calc(k, s, c):
  if (k, s, c) in dp:
    return dp[(k, s, c)]
  if k < s - 1:
    dp[(k, s, c)] = 999999999
  elif k == s - 1:
    if c == white:
      dp[(k, s, c)] = sum(a[0 : s])
    else:
      dp[(k, s, c)] = h * s - sum(a[0 : s])
  else:
    dp[(k, s, c)] = min([calc(k - s, s0, 1 - c) for s0 in range(x, y + 1)])
    if c == white:
      dp[(k, s, c)] += sum(a[k - s + 1 : k + 1])
    else:
      dp[(k, s, c)] += h * s - sum(a[k - s + 1 : k + 1])
  return dp[(k, s, c)]

h, w, x, y = map(int, input().split())
for i in range(h):
  st = str(input())
  a = [a[i] + (st[i] == '#') for i in range(w)]
  
ans = 999999999
for s in range(0, y + 1):
  g1 = calc(w - 1, s, white)
  g0 = calc(w - 1, s, black)
  if x <= s <= y:
    ans = min(ans, g0, g1)
print(ans)