#include<bits/stdc++.h>
using namespace std;
#define N 55
char s[N][N];
int n,m;
const int inf=1000000;
namespace flow
{
	const int M=2505;
	int s,t;
	struct Edge{int v,cap,nxt;};
	Edge edge[M*100];
	int fir[M*5],cur[M*5],dep[M*5],ss;
	void init() {memset(fir,0,sizeof(fir)); ss=1;}
	void addedge(int u,int v,int w)
	{
		edge[++ss]=(Edge){v,w,fir[u]}; fir[u]=ss;
		edge[++ss]=(Edge){u,0,fir[v]}; fir[v]=ss;
	}
	int bfs()
	{
		for(int i=1;i<=t;i++) dep[i]=0;
		static queue<int> q;
		dep[s]=1,q.push(s);
//		printf("%d %d\n",s,t);
		while(!q.empty())
		{
			int u=q.front(); q.pop();
			for(int i=fir[u];i!=0;i=edge[i].nxt)
			{
				if(!edge[i].cap) continue;
				int v=edge[i].v;
				if(!dep[v]) dep[v]=dep[u]+1,q.push(v);
			}
		}
		return dep[t];
	}
	int dfs(int u,int fl)
	{
		// printf("%d %d\n",u,fl);
		if(u==t||!fl) return fl;
		int ans=0;
		for(int &i=cur[u];i!=0;i=edge[i].nxt)
		{
			if(!edge[i].cap) continue;
			int v=edge[i].v;
			if(dep[v]!=dep[u]+1) continue;
			int go=dfs(v,min(fl,edge[i].cap));
			if(go)
			{
				fl-=go,ans+=go;
				edge[i].cap-=go;
				edge[i^1].cap+=go;
			}
			if(!fl) return ans;
		}
		return ans;
	}
	int dinic()
	{
		int ans=0;
		while(bfs())
		{
			for(int i=1;i<=t;i++) cur[i]=fir[i];
			ans+=dfs(s,inf);
		}
		return ans;
	}
};
using flow::addedge;
int ind[N][N],ond[N][N];
int cnt;
int gid(int x,int y) {return (x-1)*m+y;}
signed main()
{
#ifdef xay5421
	freopen("b.in","r",stdin);
#endif
	cin>>n>>m;
	for(int i=1;i<=n;i++) scanf("%s",s[i]+1);
	flow::init();
	for(int i=1;i<=n;i++) for(int j=1;j<=m;j++)
	{
		ind[i][j]=++cnt,ond[i][j]=++cnt;
		addedge(ind[i][j],ond[i][j],s[i][j]=='#');
	}
	flow::s=++cnt,flow::t=++cnt;
	for(int i=1;i<=n;i++) addedge(flow::s,ind[i][1],inf);
	for(int j=1;j<=m;j++) addedge(flow::s,ind[n][j],inf);
	for(int i=1;i<=n;i++) addedge(ond[i][m],flow::t,inf);
	for(int j=1;j<=m;j++) addedge(ond[1][j],flow::t,inf);
	for(int i=1;i<=n;i++) for(int j=1;j<=m;j++)
	{
		for(int dx=-2;dx<=2;dx++) for(int dy=-2;dy<=2;dy++)
		{
			if(dx==0&&dy==0) continue;
			int tx=i+dx,ty=j+dy;
			if(1<=tx&&tx<=n&&1<=ty&&ty<=m) addedge(ond[i][j],ind[tx][ty],inf);
		}
	}
	int ans=flow::dinic();
	cout<<ans<<endl;
	return 0;
}