#include<bits/stdc++.h>
#define FL(i,a,b) for(int i=(a);i<=(b);i++)
#define FR(i,a,b) for(int i=(a);i>=(b);i--)
#define ll long long
#define PII pair<int,int>
using namespace std;
const int MAXN = 3e3 + 10;
const int inf = 0x3f3f3f3f;
int dx[8]={0,1,0,-1,1,1,-1,-1};
int dy[8]={1,0,-1,0,-1,1,1,-1};
char c[MAXN][MAXN];
int dis[MAXN][MAXN];
int main(){
//	freopen("rufuge.in","r",stdin);
//	freopen("refuge.out","w",stdout);
	int H,W;
	scanf("%d%d",&H,&W);
	FL(i,1,H) FL(j,1,W) scanf(" %c",&c[i][j]);
	memset(dis,0x3f,sizeof(dis));
	queue<PII>q;
	FL(i,0,H+1){
		FL(j,0,W+1){
			if(i<1||i>H||j<1||j>W||c[i][j]=='.') dis[i][j]=0,q.push({i,j});
		}
	}
	int ans=0;
	while(!q.empty()){
		PII u=q.front();
		q.pop();
//		printf("(%d,%d) %d\n",u.first,u.second,dis[u.first][u.second]);
		ans=max(ans,dis[u.first][u.second]);
		FL(i,0,7){
			int x=u.first+dx[i],y=u.second+dy[i];
			if(x<1||x>H||y<1||y>W) continue;
			if(dis[x][y]>dis[u.first][u.second]+1) dis[x][y]=dis[u.first][u.second]+1,q.push({x,y}); 
		}
	}
//	FL(i,0,H+1){
//		FL(j,0,W+1) printf("%d ",dis[i][j]);
//		puts("");
//	}
	printf("%d\n",ans);
}