#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>
#include <cstring>
#include <random>
#include <functional>
#include <numeric>
#include <bitset>
#include <fstream>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)
#define all(c) (c).begin(), (c).end()
#define zero(a) memset(a, 0, sizeof a)
#define minus(a) memset(a, -1, sizeof a)
#define watch(a) { cout << #a << " = " << a << endl; }
template<class T1, class T2> inline bool minimize(T1 &a, T2 b) { return b < a && (a = b, 1); }
template<class T1, class T2> inline bool maximize(T1 &a, T2 b) { return a < b && (a = b, 1); }

typedef long long ll;
int const inf = 1<<29;

int dx[4] = {-1,0,1,0};
int dy[4] = {0,-1,0,1};
template<class T> constexpr bool in_range(T y, T x, T H, T W) { return 0<=y&&y<H&&0<=x&&x<W; }

char G[3003][3003];

int main() {

  int H, W; cin >> H >> W; cin.ignore();

  rep(i, H + 2) rep(j, W + 2) {
    G[i][j] = '.';
  }

  rep(i, H) {
    rep(j, W) {
      scanf("%c", &(G[i+1][j+1]));
    }
    cin.ignore();
  }

  H += 2, W += 2;
/*
  rep(i, H) {
    rep(j, W) {
      printf("%c", G[i][j]);
    }
    puts("");
  }
//*/

  vector<pair<int, int>> v;

  rep(i, H) rep(j, W) if(G[i][j] == '.') {
    rep(k, 4) {
      int ni = i + dy[k], nj = j + dx[k];
      if(!in_range(ni, nj, H, W)) continue;
      if(G[ni][nj] == '#') {
        v.emplace_back(i, j);
      }
    }
  }

  sort(all(v));
  v.erase(unique(all(v)), v.end());

//  for(auto && e: v) {   cout << e.first << ", " << e.second << endl; }

  int ans = 0;

  rep(i, H) rep(j, W) {
    if(G[i][j] == '#') {
      int mn = inf;
      for(auto && e: v) {
        mn = min(mn, max(abs(e.first - i), abs(e.second - j)));
      }
      ans = max(mn, ans);
    }
  }

  cout << ans << endl;
    
  return 0;
}