#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


template <class Flow> struct MaxFlow {
  // Watch out when using types other than int and long long.
  static constexpr Flow FLOW_EPS = 1e-10L;
  static constexpr Flow FLOW_INF = std::numeric_limits<Flow>::max();
  
  int n, m;
  vector<int> ptr, nxt, zu;
  vector<Flow> capa;

  explicit MaxFlow(int n_) : n(n_), m(0), ptr(n_, -1) {}
  void ae(int u, int v, Flow w0, Flow w1 = 0) {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    assert(0 <= w0);
    assert(0 <= w1);
    nxt.push_back(ptr[u]); zu.push_back(v); capa.push_back(w0); ptr[u] = m++;
    nxt.push_back(ptr[v]); zu.push_back(u); capa.push_back(w1); ptr[v] = m++;
  }

  vector<int> see, lev, que;

  Flow augment(int u, int t, Flow limFlow) {
    if (u == t) return limFlow;
    for (int &i = see[u]; ~i; i = nxt[i]) if (capa[i] > FLOW_EPS) {
      const int v = zu[i];
      if (lev[u] < lev[v]) {
        const Flow f = augment(v, t, min(limFlow, capa[i]));
        if (f > FLOW_EPS) { capa[i] -= f; capa[i ^ 1] += f; return f; }
      }
    }
    return 0;
  }
  bool bfs(int s, int t) {
    for (int u = 0; u < n; ++u) { see[u] = ptr[u]; lev[u] = -1; }
    auto head = que.begin(), tail = que.begin();
    for (lev[*tail++ = s] = 0; head != tail; ) {
      const int u = *head++;
      for (int i = ptr[u]; ~i; i = nxt[i]) if (capa[i] > FLOW_EPS) {
        const int v = zu[i];
        if (!~lev[v]) {
          lev[*tail++ = v] = lev[u] + 1;
          if (v == t) return true;
        }
      }
    }
    return false;
  }
  Flow run(int s, int t, Flow limFlow = FLOW_INF) {
    see.resize(n); lev.resize(n); que.resize(n);
    Flow flow = 0;
    for (; flow + FLOW_EPS < limFlow && bfs(s, t); ) {
      for (Flow f; (f = augment(s, t, limFlow - flow)) > FLOW_EPS; flow += f) {}
    }
    return flow;
  }
};

////////////////////////////////////////////////////////////////////////////////


/*
    3      3
   \2       
  01233333  
   12322222 
   12321112 
   122210123
   1111101\ 
  0      0  
*/

int M, N;
char A[60][60];

bool inside(int x, int y) {
  return (-2 <= x && x < M + 2 && -2 <= y && y < N + 2 && !(x < 0 && y < 0) && !(M <= x && N <= y));
}

// (b[x][y]>=1) <== (b[x][y]>=2) <== (b[x][y]>=3)
int id(int x, int y, int k) {
  return ((x + 2) * (N + 4) + (y + 2)) * 3 + (k - 1);
}

int main() {
  for (; ~scanf("%d%d", &M, &N); ) {
    for (int x = 0; x < M; ++x) {
      scanf("%s", A[x]);
    }
    
    MaxFlow<int> mf((M + 4) * (N + 4) * 3 + 2);
    const int INF = mf.FLOW_INF;
    const int s = mf.n - 2;
    const int t = mf.n - 1;
    for (int x = -2; x < M + 2; ++x) for (int y = -2; y < N + 2; ++y) if (inside(x, y)) {
      mf.ae(id(x, y, 2), id(x, y, 1), INF);
      mf.ae(id(x, y, 3), id(x, y, 2), INF);
    }
    for (int x = -2; x < M + 2; ++x) for (int y = -2; y < N + 2; ++y) if (inside(x, y)) {
      for (int dx = -1; dx <= +1; ++dx) for (int dy = -1; dy <= +1; ++dy) if (dx || dy) {
        const int xx = x + dx;
        const int yy = y + dy;
        if (inside(xx, yy)) {
          // |b[x'][y'] - b[x][y]| <= 1
          mf.ae(id(x, y, 2), id(xx, yy, 1), INF);
          mf.ae(id(x, y, 3), id(xx, yy, 2), INF);
        }
      }
    }
    for (int x = -2; x < M + 2; ++x) for (int y = -2; y < N + 2; ++y) if (inside(x, y)) {
      if (y == -2 || x == M + 1) {
        // b[x][y] = 0
        mf.ae(id(x, y, 1), t, INF);
      }
      if (x == -2 || y == N + 1) {
        // b[x][y] = 3
        mf.ae(s, id(x, y, 3), INF);
      }
    }
    for (int x = 0; x < M; ++x) for (int y = 0; y < N; ++y) if (A[x][y] == '#') {
      // cost 1 for b[x][y] \in {1, 2}
      mf.ae(id(x, y, 1), id(x, y, 3), 1);
    }
    const int ans = mf.run(s, t);
    printf("%d\n", ans);
  }
  return 0;
}