//yukicoder@cpp17

#include <iostream>
#include <iomanip>

#include <algorithm>

#include <cmath>
#include <cctype>
#include <climits>
#include <cassert>

#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>

#include <random>

#include <bitset>

#include <complex>

#include <utility>

#include <numeric>

#include <functional>


using namespace std;
using ll = long long;
using P = pair<ll,ll>;


const ll MOD = 998244353;
const ll MODx = 1000000007;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62LL)-1;
const double EPS = (1e-10);


P ar4[4] = {{0,1},{0,-1},{1,0},{-1,0}};
P ar8[8] = {{-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1}};


template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }
 
/*
確認ポイント
cout << fixed << setprecision(n) << 小数計算//n桁の小数表記になる

計算量は変わらないが楽できるシリーズ
min(max)_element(iter,iter)で一番小さい(大きい)値のポインタが帰ってくる
count(iter,iter,int)でintがiterからiterの間にいくつあったかを取得できる
*/

/* comment outed because can cause bugs
__attribute__((constructor))
void initial() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}
*/

int ans[2010][2010];
bool vis[2010][2010];
struct d{
  int y,x,d;
};

bool check(int i, int j, int h, int w){
  return 0 <= i && i <= h && 0 <= j && j <= w && !vis[i][j];
}

int main(){
  int h,w;cin>>h>>w;
  vector<string> A(h);
  for(int i = 0; h > i; i++)cin>>A[i];
  queue<d> X;
  for(int i = 0; h > i; i++){
    for(int j = 0; w > j; j++){
      if(A[i][j] == '.'){
        X.push({i+1,j+1,0});
        vis[i+1][j+1] = 1;
      }
    }
  }
  for(int i = 0; h > i; i++){
    X.push({i, 0, 0});
    X.push({i, w+1, 0});
  }
  for(int j = 0; w > j; j++){
    X.push({0,j,0});
    X.push({h+1,j,0});
  }
  int ret = 0;
  while(X.size()){
    auto z = X.front();X.pop();
    int i = z.y, j = z.x;
    ret = z.d;
    if(check(i-1,j-1,h,w)){
      vis[i-1][j-1] = true;
      ans[i-1][j-1] = z.d+1;
      X.push({i-1,j-1,z.d+1});
    }
    if(check(i-1,j,h,w)){
      vis[i-1][j] = true;
      ans[i-1][j] = z.d+1;
      X.push({i-1,j,z.d+1});
    }
    if(check(i-1,j+1,h,w)){
      vis[i-1][j+1] = true;
      ans[i-1][j+1] = z.d+1;
      X.push({i-1,j+1,z.d+1});
    }
    if(check(i,j-1,h,w)){
      vis[i][j-1] = true;
      ans[i][j-1] = z.d+1;
      X.push({i,j-1,z.d+1});
    }
    if(check(i,j+1,h,w)){
      vis[i][j+1] = true;
      ans[i][j+1] = z.d+1;
      X.push({i,j+1,z.d+1});
    }
    if(check(i+1,j-1,h,w)){
      vis[i+1][j-1] = true;
      ans[i+1][j-1] = z.d+1;
      X.push({i+1,j-1,z.d+1});
    }
    if(check(i+1,j,h,w)){
      vis[i+1][j] = true;
      ans[i+1][j] = z.d+1;
      X.push({i+1,j,z.d+1});
    }
    if(check(i+1,j+1,h,w)){
      vis[i+1][j+1] = true;
      ans[i+1][j+1] = z.d+1;
      X.push({i+1,j+1,z.d+1});
    }
  }
  cout << ret << endl;
  return 0;
}