#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,a,b) for(ll i=a-1;i>=b;i--)
#define ll long long
#define ull unsigned ll
#define ld long double
#define bl __int128_t
#define fi first
#define se second
#define vel vector<ll>
#define vvel vector<vel>
#define pll pair<ll,ll>
#define vepll vector<pll>
#define vvepll vector<vepll>
#define ves vector<string>
#define vem vector<mint>
#define vvem vector<vem>
#define pmm pair<mint,mint>
#define cleout(i) cout<<fixed<<setprecision(i)
template<class T>using PQ=priority_queue<T,vector<T>,greater<T>>;
//               上  右 下 左
vector<int> di={-1, 0, 1, 0};
vector<int> dj={ 0, 1, 0,-1};

vector<int> dx={ 0, 1, 0,-1};
vector<int> dy={ 1, 0,-1, 0};


vector<int> ddx={ 1, 1, 1, 0, -1, -1, -1, 0 };
vector<int> ddy={ 1, 0, -1, -1, -1, 0, 1, 1 };

ll inf=1000000000000000000;//1e18
// LLONG_MAX

void _solve(){
    ll N,M;
    cin>>N>>M;
    vector<ves> a(N,ves(M));
    rep(i,0,N){
        rep(j,0,M){
            cin>>a[i][j];
        }
    }
    ll ans=inf;
    rep(i,0,(1ll<<(2*N))){
        vvel b(M,vel(M));
        ll bit=i;
        auto f=[&](ves &X,ll cnt){
            ves x=X;
            ves res=x;
            rep(j,0,cnt){
                rep(k,0,M){
                    rep(l,0,M){
                        res[l][M-1-k]=x[k][l];
                    }
                }
                x=res;
            }
            rep(j,0,M){
                rep(k,0,M){
                    if(res[j][k]=='#')b[j][k]=1;
                }
            }
        };
        rep(j,0,N){
            f(a[j],bit%4);
            bit/=4;
        }
        ll sum=0;
        rep(j,0,M){
            rep(k,0,M){
                if(b[j][k])sum++;
            }
        }
        ans=min(ans,sum);
    }
    cout<<ans<<"\n";
}


int main(){
    cin.tie(nullptr);
 	ios_base::sync_with_stdio(false);

    
    ll _;
    bool multitest=0;
    if(multitest)cin>>_;
    else _=1;
    rep(__,0,_){
        _solve();
    }
}