from itertools import product

N, M = map(int, input().split())

patterns = []

for _ in range(N):
    g = [input() for _ in range(M)]
    patterns.append(g)

def rotate(g):
    return [''.join(g[M - 1 - j][i] for j in range(M)) for i in range(M)]

# 各パターンの4方向を前計算
rots = []
for g in patterns:
    tmp = []
    now = g
    for _ in range(4):
        tmp.append(now)
        now = rotate(now)
    rots.append(tmp)

ans = M * M

for dirs in product(range(4), repeat=N):
    black = 0
    for r in range(M):
        for c in range(M):
            for i in range(N):
                if rots[i][dirs[i]][r][c] == '#':
                    black += 1
                    break
    ans = min(ans, black)

print(ans)