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

int main () {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int h, w;
  int dx[] = {1, 0, -1, 0};
  int dy[] = {0, 1, 0, -1};
  char c;
  queue<pair<int, int>> q;
  cin >> h >> w;
  vector<vector<int>> v(h+2, vector<int>(w+2, 0));
  for (int i = 1; i <= h; ++i) {
    for (int j = 1; j <=w; ++j) {
      cin >> c;
      if (c == '.') v[i][j] = -1;
      else q.emplace(i, j);
    }
  }
  while (!q.empty()) {
    int y = q.front().first;
    int x = q.front().second;
    q.pop();
    for (int i = 0; i < 4; ++i) {
      if (v[y + dy[i]][x + dx[i]] == -1) {
        v[y + dy[i]][x + dx[i]] = v[y][x] + 1;
        q.emplace(y + dy[i], x + dx[i]);
      }
    }
  }
  int mx = 0;
  for (int i = 1; i <= h; ++i) {
    for (int j = 1; j <= w; ++j) {
      mx = max(mx, v[i][j]);
    }
  }
  cout << mx << endl;
}