N, M = map(int, input().split())
S = [[[["."] * M for _ in range(M)] for _ in range(4)] for _ in range(N)]

for i in range(N):
    for j in range(M):
        S[i][0][j] = list(input())


for n in range(N):
    for d in range(1,4):
        for i in range(M):
            for j in range(M):
                S[n][d][j][M-1-i] = S[n][d-1][i][j]

ans = float("inf")
for mask in range(4**N):
    tmp = 0
    for i in range(M):
        for j in range(M):
            c = 0
            x = mask
            for n in range(N):
                x, d = divmod(x,4)
                if S[n][d][i][j] == "#":
                    c = 1
            tmp += c
    ans = min(ans, tmp)

print(ans)