#include<bits/stdc++.h>
using namespace std;
constexpr int N=2505,M=1e5+5;
bool mp[55][55];
int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};
int bid,s,t,n,m,dep[N],fir[N],fr[N],nxt[M],to[M],val[M],tot;
inline void addedge(int u,int v,int w){nxt[++tot]=fir[u],fir[u]=tot,to[tot]=v,val[tot]=w;}
inline void add(int u,int v,int w){addedge(u,v,w),addedge(v,u,0);}
vector<tuple<int,int,int>> E;
inline bool bfs(){
	memset(dep,0,sizeof dep);
	memcpy(fr,fir,sizeof fr);
	queue<int> q;q.push(s);dep[s]=1;
	while(!q.empty()){
		int p=q.front();q.pop();
		if(p==t) return 1;
		for(int i=fr[p];i;i=nxt[i])if(val[i]&&!dep[to[i]]) dep[to[i]]=dep[p]+1,q.push(to[i]);
	}
	return 0;
}
int dinic(int p,int res){
	if(p==t) return res;
	int fl=0;
	for(int &i=fr[p];i;i=nxt[i])if(val[i]&&dep[to[i]]==dep[p]+1){
		int z=dinic(to[i],min(res,val[i]));
		val[i]-=z,val[i^1]+=z,fl+=z,res-=z;
	}
	if(!fl) dep[p]=0;
	return fl;
}
inline int calc(){
	memset(fir,0,sizeof fir);tot=1;
	for(auto [u,v,w]:E) if(u!=bid&&v!=bid) add(u,v,w);
	int res=0;
	while(bfs()) res+=dinic(s,1e9);
	return res;
}
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		string s;cin>>s;
		for(int j=0;j<m;j++) mp[i][j+1]=s[j]=='.';
	}
	auto f=[&](int x,int y){return (x-1)*m+y;};
	s=0,t=n*m+1;
	for(int i=1;i<=n;i++)
	for(int j=1;j<=m;j++)if(mp[i][j]){
		if(i+j&1){
			E.emplace_back(s,f(i,j),1);
			for(int d=0;d<4;d++){
				int x=i+dx[d],y=j+dy[d];
				if(x>=1&&y>=1&&x<=n&&y<=m&&mp[x][y]) E.emplace_back(f(i,j),f(x,y),1);
			}
		}
		else E.emplace_back(f(i,j),t,1);
	}
	bid=-1;
	int all=calc(),ans=0;
	for(int i=1;i<=n*m;i++) if(mp[(i-1)/m+1][(i-1)%m+1])bid=i,ans+=calc()==all;
	cout<<ans<<'\n';
}