#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second 

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

mt19937 rng;

struct Graph
{
	int szL, szR;
	vector<VI> g;
	VI mateForR, mateForL, usedL;
	
	void init(int L, int R)
	{
		szL = L, szR = R;
		g.resize(szL);
		mateForL.resize(szL);
		usedL.resize(szL);
		
		mateForR.resize(szR);
	}
	
	void addEdge(int from, int to)
	{
		assert(0 <= from && from < szL);
		assert(0 <= to && to < szR);
		g[from].PB(to);
	}
	
	int iter;
	bool kuhn(int v)
	{
		if (usedL[v] == iter) return false;
		usedL[v] = iter;
		shuffle(ALL(g[v]), rng);
		for (int to : g[v])
		{
			if (mateForR[to] == -1)
			{
				mateForR[to] = v;
				mateForL[v] = to;
				return true;
			}
		}
		for (int to : g[v])
		{
			if (kuhn(mateForR[to]))
			{
				mateForR[to] = v;
				mateForL[v] = to;
				return true;
			}
		}
		return false;
	}
	
	int doKuhn(int ban)
	{
		fill(ALL(mateForR), -1);
		fill(ALL(mateForL), -1);
		fill(ALL(usedL), -1);
		
		
		int res = 0;
		iter = 0;
		
		while(true)
		{
			iter++;
			if (ban != -1)
				usedL[ban] = iter;
			
			bool ok = false;
			FOR (v, 0, szL)
			{
				if (mateForL[v] == -1)
				{
					if (kuhn(v))
					{
						ok = true;
						res++;
					}
				}
			}
			if (!ok) break;
		}
		return res;
	}
};


int n, m;

bool ok(int x, int y)
{
	return 0 <= x && x < n && 0 <= y && y < m;
}

vector<PII> d = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n >> m;
	vector<string> v(n);
	FOR (i, 0, n)
		cin >> v[i];
	Graph g;
	g.init(n * m, n * m);
	FOR (i, 0, n)
	{
		FOR (j, 0, m)
		{
			for (auto [dx, dy] : d)
			{
				int ni = i + dx, nj = j + dy;
				if (ok(ni, nj) && v[i][j] != '#' && v[ni][nj] != '#')
					g.addEdge(i * m + j, ni * m + nj);
			}
		}
	}
	int ans = 0;
	int par = g.doKuhn(-1);
	FOR (i, 0, n)
	{
		FOR (j, 0, m)
		{
			if (v[i][j] == '#')
				continue;
			int x = g.doKuhn(i * m + j);
			if (x == par)
				ans++;
		}
	}
	cout << ans << '\n';
	
	
	return 0;
}