#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 MAX_H = 3000;
const int MAX_W = 3000;

int max_dist[MAX_H + 2][MAX_W + 2];

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;
  memset(max_dist, -1, sizeof(max_dist));
  vector<string> S;

  for (int y = 1; y <= H; ++y) {
    string row;
    cin >> row;
    S.push_back(row);
    for (int x = 1; x <= W; ++x) {
      if (row[x - 1] == '.') {
        max_dist[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) {
        max_dist[y][x] = 0;
      }
    }
  }

  int ans = 1;

  for (int y = 1; y <= H; ++y) {
    for (int x = 1; x <= W; ++x) {
      if (S[y - 1][x - 1] == '.') continue;

      int d1 = max(0, max_dist[y - 1][x - 1]);
      int d2 = max(0, max_dist[y - 1][x]);
      int d3 = max(0, max_dist[y][x - 1]);

      max_dist[y][x] = min(d1, min(d2, d3)) + 1;
      ans = max(ans, max_dist[y][x]);
    }
  }

  cout << (ans + 1) / 2 << endl;

  return 0;
}