#include <bits/stdc++.h>
using namespace std;

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define ALL(x) (x).begin(), (x).end()
#define BIT(n) (1LL<<(n))
#define SZ(x) ((int)(x).size())
#define fst first
#define snd second
typedef vector<int> vi;typedef vector<vi> vvi;typedef pair<int,int> pii;typedef vector<pii> vpii;
typedef long long ll;

int H, W;
int D[3000][3000];
string M[3000];

int DY[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int DX[8] = {0, 1, 0, -1, 1, -1, 1, -1};

template<typename T> inline bool inside(T y, T x, T h, T w) { return 0 <= y && y < h && 0 <= x && x < w; };

void Main() {
  cin >> H >> W;
  rep(y,H) cin >> M[y];

  memset(D, 0x3f, sizeof(D));

  priority_queue<pair<int, pii>, vector<pair<int, pii>>, greater<pair<int, pii>> > q;

  rep(y,H) {
    if (M[y][0] != '.') {
      D[y][0] = 1;
      q.push({1, {y,0}});
    }
    if (M[y][W-1] != '.') {
      D[y][W-1] = 1;
      q.push({1, {y,W-1}});
    }
  }

  rep(x,W) {
    if (M[0][x] != '.') {
      D[0][x] = 1;
      q.push({1, {0,x}});
    }
    if (M[H-1][x] != '.') {
      D[H-1][x] = 1;
      q.push({1, {H-1,x}});
    }
  }

  rep(y,H) rep(x,W) {
    if (M[y][x] == '.') {
      D[y][x] = 0;
      q.push({0,{y,x}});
    }
  }

  while (!q.empty()) {
    int c = q.top().first;
    int y = q.top().second.first;
    int x = q.top().second.second;
    q.pop();

    if (D[y][x] < c) continue;

    rep(i, 8) {
      int ny = y + DY[i];
      int nx = x + DX[i];
      if (!inside(ny, nx, H, W)) continue;
      int nc = c + 1;
      if (D[ny][nx] > nc) {
        D[ny][nx] = nc;
        q.push({nc, {ny, nx}});
      }
    }
  }

  int ma = 0;
  rep(y,H) {
    rep(x,W) {
      //_p(" %d", D[y][x]);
      ma = max(ma, D[y][x]);
    }
    //_p("\n");
  }
  _p("%d\n", ma);
}
int main() { cin.tie(0); ios::sync_with_stdio(false); Main(); return 0; }