#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int h, w; cin >> h >> w;
  h += 2; w += 2;
  vector s(h, vector(w, '.')); FOR(i, 1, h - 1) FOR(j, 1, w - 1) cin >> s[i][j];
  vector dist(h, vector(w, -1));
  vector<pair<int, int>> que;
  REP(i, h) REP(j, w) {
    if (s[i][j] == '.') {
      dist[i][j] = 0;
      que.emplace_back(i, j);
    }
  }
  for (int d = 1; !que.empty(); ++d) {
    vector<pair<int, int>> nx;
    for (auto [i, j] : que) {
      REP(k, 8) {
        int y = i + dy8[k], x = j + dx8[k];
        if (0 <= y && y < h && 0 <= x && x < w && dist[y][x] == -1) {
          dist[y][x] = d;
          nx.emplace_back(y, x);
        }
      }
    }
    que.swap(nx);
  }
  int ans = 0;
  REP(i, h) chmax(ans, *max_element(ALL(dist[i])));
  cout << ans << '\n';
  return 0;
}