#include <bits/stdc++.h>
using namespace std;

const short inf = 3e4;

using PP = pair<short, short>;
int h, w;
short a[3002][3002];
string s[3002];
int main() {
  cin >> h >> w;
  s[0] = string(w + 2, '.');
  s[h + 1] = string(w + 2, '.');
  for (int i = 0; i < h; ++i) {
    string t;
    cin >> t;
    s[i + 1] = '.' + t + '.';
  }
  
  for (int i = 0; i < h + 2; ++i) {
    for (int j = 0; j < w + 2; ++j) {
      a[i][j] = inf;
    }
  }
  
  queue<pair<short, PP>> q;
  for (int i = 0; i < h + 2; ++i) {
    for (int j = 0; j < w + 2; ++j) {
      if (i == 0 || i == h + 1
       || j == 0 || j == w + 1
       || s[i][j] == '.') {
        q.push(make_pair(0, PP(i, j)));
      }
    }
  }
  
  const int di[] = { -1, -1, -1, 0, 0, 1, 1, 1 };
  const int dj[] = { -1, 0, 1, -1, 1, -1, 0, 1 };
  while (!q.empty()) {
    auto p = q.front(); q.pop();
    short d = p.first;
    int i = p.second.first;
    int j = p.second.second;
    if (a[i][j] != inf) continue;
    a[i][j] = d;
    
    for (int k = 0; k < 8; ++k) {
      int ni = i + di[k];
      int nj = j + dj[k];
      if (ni < 0 || ni >= h + 2) continue;
      if (nj < 0 || nj >= w + 2) continue;
      q.push(make_pair(d + 1, PP(ni, nj)));
    }
  }
  
  short mx = 0;
  for (int i = 0; i < h + 2; ++i) {
    for (int j = 0; j < w + 2; ++j) {
      mx = max(mx, a[i][j]);
    }
  }
  cout << mx << endl;
}