#include<bits/stdc++.h>
using namespace std;
const int INF = 1 << 30;

int H, W;
string S[3003];
int dist[3004][3004];

int main()
{

  cin >> H >> W;
  for(int i = 1; i <= H; i++) {
    cin >> S[i];
    S[i] = "." + S[i] + ".";
  }
  S[0] = S[H + 1] = string(W + 2, '.');

  int ret = 0;
  fill_n(*dist, 3004 * 3004, INF);
  for(int i = 0; i <= H + 1; i++) {
    for(int j = 0; j <= W + 1; j++) {
      if(S[i][j] == '.') dist[i][j] = 0;
    }
  }
  for(int i = 1; i <= H; i++) {
    for(int j = 1; j <= W; j++) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j + 1] + 1);
      }
    }
    
  }
  for(int i = H; i > 0; i--) {
    for(int j = W; j > 0; j--) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j - 1] + 1);
      }
    }
  }
    for(int i = 1; i <= H; i++) {
    for(int j = 1; j <= W; j++) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j + 1] + 1);
      }
    }
    
  }
  for(int i = H; i > 0; i--) {
    for(int j = W; j > 0; j--) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j - 1] + 1);
      }
    }
  }
    for(int i = 1; i <= H; i++) {
    for(int j = 1; j <= W; j++) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j - 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i - 1][j + 1] + 1);
      }
    }
    
  }
  for(int i = H; i > 0; i--) {
    for(int j = W; j > 0; j--) {
      if(S[i][j] == '#') {
        dist[i][j] = min(dist[i][j], dist[i][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j + 1] + 1);
        dist[i][j] = min(dist[i][j], dist[i + 1][j - 1] + 1);
        ret = max(ret, dist[i][j]);
      }
    }
  }
  cout << ret << endl;
}