# haru: pypy
import sys
input = sys.stdin.readline
II = lambda : int(input())
MI = lambda : map(int, input().split())
LI = lambda : [int(a) for a in input().split()]
SI = lambda : input().rstrip()
LLI = lambda n : [[int(a) for a in input().split()] for _ in range(n)]
LSI = lambda n : [input().rstrip() for _ in range(n)]
MI_1 = lambda : map(lambda x:int(x)-1, input().split())
LI_1 = lambda : [int(a)-1 for a in input().split()]

mod = 998244353
inf = 1001001001001001001
ordalp = lambda s : ord(s)-65 if s.isupper() else ord(s)-97
ordallalp = lambda s : ord(s)-39 if s.isupper() else ord(s)-97
yes = lambda : print("Yes")
no = lambda : print("No")
yn = lambda flag : print("Yes" if flag else "No")

prinf = lambda ans : print(ans if ans < 1000001001001001001 else -1)
alplow = "abcdefghijklmnopqrstuvwxyz"
alpup = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
alpall = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
URDL = {'U':(-1,0), 'R':(0,1), 'D':(1,0), 'L':(0,-1)}
DIR_4 = [[-1,0],[0,1],[1,0],[0,-1]]
DIR_8 = [[-1,0],[-1,1],[0,1],[1,1],[1,0],[1,-1],[0,-1],[-1,-1]]
DIR_BISHOP = [[-1,1],[1,1],[1,-1],[-1,-1]]
prime60 = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59]
sys.set_int_max_str_digits(0)
# sys.setrecursionlimit(10**6)
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')

from collections import defaultdict,deque
from heapq import heappop,heappush
from bisect import bisect_left,bisect_right
DD = defaultdict
BSL = bisect_left
BSR = bisect_right

def transpose_table(mat):
    """
    転置行列
    """
    return [list(x) for x in zip(*mat)]

def rotate_table(table):
    """
    反時計回りに回転
    """
    return list(map(list, zip(*table)))[::-1]

from copy import deepcopy

n, m = MI()
s = [LSI(m) for i in range(n)]

rot = []
for i in range(n):
    rot.append([])
    t = s[i][:]
    for _ in range(4):
        t = rotate_table(t)
        rot[-1].append(deepcopy(t))

# print(rot)

ans = inf
for bit in range(1 << (2 * n)):
    p = [[0] * m for i in range(m)]
    for d in range(n):
        f = bit >> (2 * d) & 3
        for i in range(m):
            for j in range(m):
                if rot[d][f][i][j] == "#":
                    p[i][j] += 1
    
    c = 0
    for i in range(m):
        for j in range(m):
            c += p[i][j] != 0
    ans = min(ans, c)

print(ans)