#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

const int DY[4] = {-1, 0, 1, 0};
const int DX[4] = {0, 1, 0, -1};

struct Node {
  int by;
  int bx;
  int y;
  int x;
  int dist;

  Node(int by = -1, int bx = -1, int y = -1, int x = -1, int dist = -1) {
    this->by = by;
    this->bx = bx;
    this->y = y;
    this->x = x;
    this->dist = dist;
  }

  bool operator>(const Node &n) const {
    return dist > n.dist;
  }
};

int main() {
  int H, W;
  cin >> H >> W;
  priority_queue <Node, vector<Node>, greater<Node>> pque;
  int max_dist[H + 2][W + 2];
  memset(max_dist, -1, sizeof(max_dist));
  int ans = 0;

  for (int y = 1; y <= H; ++y) {
    string row;
    cin >> row;
    for (int x = 1; x <= W; ++x) {
      if (row[x - 1] == '.') {
        pque.push(Node(y, x, y, x, 0));
      }
    }
  }

  for (int y = 0; y < H + 2; ++y) {
    for (int x = 0; x < W + 2; ++x) {
      if (y == 0 || x == 0 || y == H + 1 || x == W + 1) {
        pque.push(Node(y, x, y, x, 0));
      }
    }
  }

  while (not pque.empty()) {
    Node node = pque.top();
    pque.pop();

    if (max_dist[node.y][node.x] != -1 && max_dist[node.y][node.x] <= node.dist) continue;
    max_dist[node.y][node.x] = node.dist;
    ans = max(ans, node.dist);

    for (int direct = 0; direct < 4; ++direct) {
      int ny = node.y + DY[direct];
      int nx = node.x + DX[direct];
      if (ny < 0 || H <= ny || nx < 0 || W <= nx) continue;
      int nd = max(abs(ny - node.by), abs(nx - node.bx));

      pque.push(Node(node.by, node.bx, ny, nx, nd));
    }
  }

  cout << ans << endl;

  return 0;
}