def rotateR(A):
    return list(map(list, zip(*A[::-1])))

INF = 1<<60

N, M = map(int, input().split())
S = []
for _ in range(N):
    S.append([list(input()) for _ in range(M)])

def func(idx, F):
    if idx == N:
        return sum(sum(f) for f in F)
    ans = INF
    for _ in range(4):
        NF = [f[:] for f in F]
        for i in range(M):
            for j in range(M):
                if S[idx][i][j] == "#":
                    NF[i][j] = True
        ans = min(ans, func(idx+1, NF))
        S[idx] = rotateR(S[idx])
    return ans

print(func(0, [[False]*M for _ in range(M)]))