#include<cstdio>
#include<queue>
using namespace std;
const int N=3010,dx[5]={0,1,-1,0,0},dy[5]={0,0,0,1,-1}; char s[N][N]; bool vis[N][N];
struct P { int x,y,d; };
int main() {
  //freopen("refuge.in","r",stdin);
  //freopen("refuge.out","w",stdout);
  int n,m; scanf("%d %d",&n,&m);
  for(int i=0;i<=m+1;i++) s[0][i]=s[n+1][i]='.';
  for(int i=1;i<=n;i++) scanf("%s",s[i]+1),s[i][0]=s[i][m+1]='.';
  queue<P>q;
  for(int i=0;i<=n+1;i++) for(int j=0;j<=m+1;j++) if(s[i][j]=='.') q.push((P){i,j,0}),vis[i][j]=true;
  int ans=0;
  while(!q.empty()) {
  	P p=q.front(); q.pop();
  	for(int i=1;i<=4;i++) {
  	  int xx=p.x+dx[i],yy=p.y+dy[i];
  	  if(xx>=0&&xx<=n+1&&yy>=0&&yy<=m+1&&!vis[xx][yy]) q.push((P){xx,yy,p.d+1}),vis[xx][yy]=true,ans=max(ans,p.d);
	}
  }
  printf("%d",ans);
  return 0;
}