import sys
input = sys.stdin.readline

from copy import deepcopy

N,M=list(map(int,input().split()))

S=[[list(input().strip()) for i in range(M)] for i in range(N)]

ANS=1<<63

for i in range(4**(N-1)):
    X=deepcopy(S[0])

    x=i
    for j in range(1,N):
        if x%4==0:
            for k in range(M):
                for l in range(M):
                    if S[j][k][l]=="#":
                        X[k][l]="#"
        elif x%4==1:
            for k in range(M):
                for l in range(M):
                    if S[j][k][l]=="#":
                        X[l][M-1-k]="#"
        elif x%4==2:
            for k in range(M):
                for l in range(M):
                    if S[j][k][l]=="#":
                        X[M-1-k][M-1-l]="#"
        elif x%4==3:
            for k in range(M):
                for l in range(M):
                    if S[j][k][l]=="#":
                        X[M-1-l][k]="#"

        x//=4

    #for x in X:
    #    print(x)

    #print()

    count=0

    for j in range(M):
        for k in range(M):
            if X[j][k]=="#":
                count+=1

    ANS=min(ANS,count)

print(ANS)