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

ans = 10**18
now = [[0 for _ in range(M)] for _ in range(M)]
def f(n):
    if(n == N):
        global ans
        ans = min(ans, sum(sum(now[i][j] > 0 for j in range(M)) for i in range(M)))
        return

    SS = tiles[n][:]
    for _ in range(4):
        SS = list(zip(*SS[::-1]))
        for i in range(M):
            for j in range(M):
                if(SS[i][j] == "."):continue
                now[i][j] += 1

        f(n+1)
        for i in range(M):
            for j in range(M):
                if(SS[i][j] == "."):continue
                now[i][j] -= 1

f(0)
print(ans)