#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <queue>
#include "math.h"
#include <complex>
#include <iomanip>
#include <map>
#define ifor(i,a,b) for (int i=(a);i<(b);i++)
#define rfor(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define rep(i,n) for (int i=0;i<(n);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
using namespace std;
typedef long double ld;
typedef long long int  lli;
typedef pair<int,int> P;
const double eps = 1e-11;
int vex[4]={1,0,-1,0};
int vey[4]={0,1,0,-1};
typedef vector<double> Vec;
typedef vector<int> vec;
typedef vector<Vec> MAT;
typedef vector<vec> mat;
lli MOD=1000000007;
int main(){
  int H,W;
  cin >> H >> W;
  bool fi[3004][3004];
  bool dis [3004][3004];
  queue<pair<P,int> > que;
  rep(i,H+2){
    rep(j,W+2){
      if(j==W+1||j==0||i==0||i==H+1)que.push(make_pair(P(i,j),0));
    }
  }
  char c;
  rep(i,H)rep(j,W){
    cin>>c;
  if(c=='#')fi[i+1][j+1]=true;
    if(c=='.')que.push(make_pair(P(i+1,j+1),0));
  }
  int ans = 0;
  while(!que.empty()){
    P p= que.front().first;
    int d = que.front().second;
    ans = max(ans,que.front().second);
    que.pop();
    for(int i = -1;i<=1;i++){
      for(int j = -1;j<=1;j++){
        if(p.first+i<0||p.second +j<0)continue;
        if(!(i==0&&j==0)&&!dis[p.first+i][p.second+j]&&fi[p.first+i][p.second+j]){
          dis[p.first+i][p.second+j]=true;
          que.push(make_pair(P(i+p.first,j+p.second),d+1));
        }
      }
    }
  }
  cout<<ans<<endl;
}