n, m = list(map(int, input().split()))
ans = 1<<60
S = [[[input() for _ in range(m)] for _ in range(n)]]
def cal(S0):
    T = []
    for _ in range(n):
        T.append([[S0[_][x][m-1-y] for x in range(m)] for y in range(m)])
    return T
for _ in range(3):
    S.append(cal(S[-1]))
for bit in range(1<<(2*n)):
    A = [[0 for _ in range(m)] for _ in range(m)]
    for i in range(n):
        s = (bit >> 2*i) & 3
        for y in range(m):
            for x in range(m):
                if S[s][i][y][x] == "#":
                    A[y][x] = 1
    ans = min(sum([sum(aa) for aa in A]), ans)
print(ans)