#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[8] = {-1,0,1,0,-1,1,1,-1};
int dy[8] = {0,-1,0,1,-1,-1,1,1};
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[3010][3010];
int dist[3010][3010];

int main() {

  cin.tie(0);
  ios::sync_with_stdio(false);

  int H, W; cin >> H >> W;
  rep(i, H + 2) {
    if(i == 0 || i == H + 1) rep(j, W + 2) G[i][j] = '.';
    else {
      cin >> (G[i] + 1);
      G[i][0] = G[i][W+1] = '.';
    }
  }

  H += 2, W += 2;

  queue<tuple<int, int, int>> q;

  rep(i, H) rep(j, W) {
    dist[i][j] = inf;
    if(G[i][j] == '.') dist[i][j] = 0, q.emplace(0, i, j);
  }

  int max = 0;

  while(!q.empty()) {
    int c, y, x; tie(c, y, x) = q.front(); q.pop();
    rep(k, 8) {
      int ny = y + dy[k], nx = x + dx[k];
      if(!in_range(ny, nx, H, W)) continue;
      if(dist[ny][nx] > c + 1) {
        dist[ny][nx] = c + 1;
        maximize(max, c + 1);
        q.emplace(c + 1, ny, nx);
      }
    }
  }

  cout << max << endl;

  return 0;
}