긍정적 사고, 음식의 절제, 규칙적인 운동

import sys

N, M = map(int, sys.stdin.readline().split())

board = []
white_first = []
black_first = []

for _ in range(N):
    row = sys.stdin.readline().replace("\n", "")
    board.append([i for i in row])

initial_color = board[0][0]

# 흰색으로 시작하는 체스판을 만들 경우
for index, row in enumerate(board):
    painting = []
    if index % 2 == 0: current_color = "W"
    else: current_color = "B"

    for value in row:
        if value == current_color: painting.append(0)
        else: painting.append(1)
        
        if current_color == "W": current_color = "B"
        else: current_color = "W"
    white_first.append(painting)

# 검은색으로 시작하는 체스판을 만들 경우
for index, row in enumerate(board):
    painting = []
    if index % 2 == 0: current_color = "B"
    else: current_color = "W"

    for value in row:
        if value == current_color: painting.append(0)
        else: painting.append(1)
        
        if current_color == "W": current_color = "B"
        else: current_color = "W"
    black_first.append(painting)

# 최솟값을 초기화 할 때, 보드의 최대 크기인 50*50 = 2500으로 한다.
min_count = 2500
for i in range(N-8+1):
    rows = white_first[i:i+8]
    for j in range(M-8+1):
        paint = 0
        for row in rows:
            paint += sum(row[j:j+8])
        if paint < min_count: min_count = paint

for i in range(N-8+1):
    rows = black_first[i:i+8]
    for j in range(M-8+1):
        paint = 0
        for row in rows:
            paint += sum(row[j:j+8])
        if paint < min_count: min_count = paint

print(min_count)

# 참조 : https://nerogarret.tistory.com/35