#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001


int main(){
	
	int h,w;
	cin>>h>>w;
	
	vector<string> s(h);
	rep(i,h)cin>>s[i];
	
	vector d(h,vector<int>(w,Inf32));
	deque<pair<int,int>> D;
	for(int i=h-3;i<h;i++){
		rep(j,w-3){
			if(s[i][j]=='#'){
				d[i][j] = 0;
				D.emplace_back(i,j);
			}
			else{
				d[i][j] = 1;
				D.emplace_front(i,j);
			}
		}
	}
	for(int i=3;i<h;i++){
		rep(j,3){
			if(s[i][j]=='#'){
				d[i][j] = 0;
				D.emplace_back(i,j);
			}
			else{
				d[i][j] = 1;
				D.emplace_front(i,j);
			}
		}
	}
	while(D.size()>0){
		int x = D.back().first,y = D.back().second;
		D.pop_back();
		for(int i=-3;i<=3;i++){
			for(int j=-3;j<=3;j++){
				int xx = x+i,yy = y+j;
				if(xx<0||xx>=h||yy<0||yy>=w)continue;
				int cost = d[x][y];
				if(s[xx][yy]=='.')cost++;
				if(xx<3&&yy<3)continue;
				if(xx>=h-3&&yy>=w-3)continue;
				if(d[xx][yy]<=cost)continue;
				d[xx][yy] = cost;
				if(s[xx][yy]=='.'){
					D.emplace_front(xx,yy);
				}
				else D.emplace_back(xx,yy);
			}
		}
	}
	int ans = Inf32;
	rep(i,h-3){
		for(int j=w-3;j<w;j++){
			
			ans =min(ans,d[i][j]);
		}
	}
	rep(i,3){
		for(int j=3;j<w;j++){
			ans = min(ans,d[i][j]);
		}
	}
	cout<<ans<<endl;
	
	
	return 0;
}