from copy import deepcopy
from itertools import product


def rotate(grid):
    return [*zip(*grid[::-1])]


N, M = [int(s) for s in input().split()]
grids = []
for _ in range(N):
    grid = [[*input()] for _ in range(M)]
    grids.append(grid)

rotates = []

for i in range(4):
    G = deepcopy(grids)
    for _ in range(i):
        new_grids = []
        for g in G:
            new_grids.append(rotate(g))
        G = new_grids
    rotates.append(G)

ans = M**2

for indexes in product(range(4), repeat=N):
    count = 0

    for i in range(M):
        for j in range(M):
            for k in range(N):
                if rotates[indexes[k]][k][i][j] == "#":
                    count += 1
                    break

    ans = min(ans, count)

print(ans)