# 再帰関数解法 (愚直解)
N, M = map(int, input().split())
S = []
for i in range(N):
    S.append([list(input()) for _ in range(M)])

import sys
sys.setrecursionlimit(10**6) # 足りないかもしれない

def rotate_90(grid: list[list]) -> list[list]:
    """概要:
        2次元配列を時計回りに90度回転して返す。
    入力:
        grid (list[list]): 元グリッド。
    出力:
        list[list]: 回転後グリッド。
    補足:
        計算量は O(HW)。
    """
    H, W = len(grid), len(grid[0])
    return [[grid[H - 1 - j][i] for j in range(H)] for i in range(W)]

answer = 10**9

from collections import Counter
def f(Map, N, ans = 105, S = S):
    if N == 0:
        ans = sum([s[1] for s in [Counter(s) for s in Map]])
        return ans
    N -= 1
    tmp = 105
    for i in range(4):
        S[N] = rotate_90(S[N])
        NMap = [row[:] for row in Map]
        for j in range(M):
            for k in range(M):
                if S[N][j][k] == '#':
                    NMap[j][k] = 1
        tmp = min(tmp, f(NMap, N))
    return tmp

answer = f([[0]*M for _ in range(M)], N)
print(answer)