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 "#".
'''
# Submitted By M7moud Ala3rj
Don't Copy This Code, CopyRight . [email protected] © 2022-2023 :)
'''
# Problem Name = "Barcode"
# Class: C

from collections import defaultdict
from sys import stdin, stdout

input = stdin.readline
def print(*args, end='\n', sep=' ') -> None:
    stdout.write(sep.join(map(str, args)) + end)

def minus(): return -1

d = defaultdict(minus)

def func(i=0, p="", r=0):
    global n, m, x, y, lst
    ans = d[(i, p, r)]
    if ans != -1:
        return ans
    if i==m: return 0 if x<=r<=y else float("inf")
    hashes = lst[i] ; dots = n-hashes
    if r<x:
        if p==1:
            ans = func(i+1, 1, r+1)+dots ; d[(i, p, r)] = ans
            return ans
        ans = func(i+1, 0, r+1)+hashes ; d[(i, p, r)] = ans
        return ans
    elif r==y:
        if p==1:
            ans = func(i+1, 0, 1)+hashes ; d[(i, p, r)] = ans
            return ans
        ans = func(i+1, 1, 1)+dots ; d[(i, p, r)] = ans
        return ans
    else:
        ans = min(func(i+1, 1, (r+1)*(1==p)+(1!=p))+dots, func(i+1, 0, (r+1)*(0==p)+(0!=p))+hashes) ; d[(i, p, r)] = ans
        return ans

import os,sys
from io import BytesIO, IOBase
 
def main():
    global n, m, x, y, lst
    n, m, x, y = list(map(int, input().split()))
    lst = [0]*m ; z = [input().strip() for i in range(n)]
    for s in z:
        for o in range(m): lst[o]+=(s[o]=="#")
        
    ans = min(func(1, 1, 1)+(n-lst[0]), func(1, 0, 1)+lst[0])
    print(ans)
 
# Fast IO Region
BUFSIZE = 8192
class FastIO(IOBase):
    newlines = 0
    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None
    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()
    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()
    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)
class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")
sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")
if __name__ == "__main__":
    main()