#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i ++)
#define rep1(i, n) for(int i = 1; i <= (int)(n); i ++)
#define MP make_pair
 
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;

namespace fl {
    const LL INF = 0x3f3f3f3f3f3f3f3fLL;
    int vn, en;
    pair<int, LL> E[300005];
    vector<int> G[300005];
    int dis[300005];
    void adde(int u, int v, LL w)
    {
        E[en] = MP(v, w);
        G[u].push_back(en ++);
        E[en] = MP(u, 0);
        G[v].push_back(en ++);
    }
    
    int pos[300005], que[300005], fr, rr;
    bool bfs(int v, int t)
    {
        rep(i, vn) {
            pos[i] = 0; dis[i] = -1;
        }
        fr = rr = 0;
        dis[v] = 0;
        que[rr ++] = v;
        while(fr < rr) {
            v = que[fr ++];
            rep(i, G[v].size()) {
                int ce = G[v][i];
                if(E[ce].second == 0) continue;
                if(dis[E[ce].first] == -1) {
                    dis[E[ce].first] = dis[v] + 1;
                    que[rr ++] = E[ce].first;
                }
            }
        }
        return dis[t] != -1;
    }
    LL dfs(int s, int t, LL tot = INF)
    {
        if(s == t) return tot;
        LL ret = 0;
        for(; pos[s] < (int)G[s].size(); pos[s] ++) {
            int ce = G[s][pos[s]];
            if(E[ce].second > 0 && dis[E[ce].first] == dis[s] + 1) {
                LL cf = min(E[ce].second, tot);
                cf = dfs(E[ce].first, t, cf);
                tot -= cf; ret += cf;
                E[ce].second -= cf; E[ce ^ 1].second += cf;
            }
            if(tot == 0) break;
        }
        return ret;
    }
    LL maxf(int s, int t)
    {
        LL ret = 0;
        while(bfs(s, t)) ret += dfs(s, t);
        return ret;
    }
}

const int INF = 0x3f3f3f3f;
char gr[55][55];
int n, m, ver[55][55][2], vn;
LL ans;

int main() {
    scanf("%d%d", &n, &m);
    for(int i = 0; i < n; i++) scanf("%s", gr[i]);
    vn = 2;
    for(int i = 0; i <= n; i++) for(int j = 0; j <= m; j++) for(int k = 0; k < 2; k++) ver[i][j][k] = vn++;

    for(int i = 0; i <= n; i++) for(int j = 0; j <= m; j++) {
        fl::adde(0, ver[i][j][0], INF * (i == 0 || j == m ? 2 : 1));
        fl::adde(ver[i][j][0], ver[i][j][1], INF);
        fl::adde(ver[i][j][1], 1, INF * (i == n || j == 0 ? 2 : 1));
        ans += INF;
    }
    for(int i = 0; i <= n; i++) for(int j = 0; j <= m; j++)
        for(int di = -1; di <= 1; di++) for(int dj = -1; dj <= 1; dj++)
            if(i + di >= 0 && i + di <= n && j + dj >= 0 && j + dj <= m)
                fl::adde(ver[i][j][1], ver[i + di][j + dj][0], INF);
    for(int i = 0; i < n; i++) for(int j = 0; j < m; j++) if(gr[i][j] == '#') {
        for(int di = 0; di < 2; di++) for(int dj = 0; dj < 2; dj++) {
            fl::adde(ver[i + di][j + dj][0], vn, INF);
        }
        fl::adde(vn, 1, 1);
        vn++;
        for(int di = 0; di < 2; di++) for(int dj = 0; dj < 2; dj++) {
            fl::adde(vn, ver[i + di][j + dj][1], INF);
        }
        fl::adde(0, vn, 1);
        vn++;
        ans++;
    }
    fl::vn = vn;
    ans = fl::maxf(0, 1) - ans;
    printf("%lld\n", ans);
    return 0;
}