#include<bits/stdc++.h>
using namespace std;
const int N=3010;
int n,m,ans,dis[N][N];
string a[N];
queue<int> q;
signed main(){
	ios::sync_with_stdio(0);
	cin>>n>>m;
	for(int i=0;i<=m+1;i++){
		a[0][i]='.';
		a[n+1][i]='.';
	}
	for(int i=1;i<=n;i++){
		cin>>a[i];
		a[i]="."+a[i]+".";
	}
	memset(dis,0x3f,sizeof(dis));
	for(int i=0;i<=n+1;i++){
		for(int j=0;j<=m+1;j++){
			if(a[i][j]=='.') dis[i][j]=0,q.push(i*N+j);
		}
	}
	while(!q.empty()){
		int now=q.front(),i=now/N,j=now%N;
		q.pop();
		for(int nxt=0;nxt<=8;nxt++){
			int ni=i+(nxt/3-1),nj=j+(nxt%3-1);
			if(ni<0||ni>n+1||nj<0||nj>m+1) continue;
			if(dis[ni][nj]>dis[i][j]+1){
				dis[ni][nj]=dis[i][j]+1;
				ans=max(ans,dis[ni][nj]);
				q.push(ni*N+nj);
			} 
		}
	}
	cout<<ans<<'\n';
	return 0;
}