#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()
#define printV(v) for(auto&& x : v){cerr << x << " ";} cerr << endl
#define printVV(vv) for(auto&& v : vv){for(auto&& x : v){cerr << x << " ";}cerr << endl;}

typedef long long ll;
typedef pair<int, int> Pii;
typedef pair<ll, ll> Pll;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;
typedef vector<vector<int>> Graph;
const int inf = 1e9;
const int mod = 1e9 + 7;

VV rot(const VV& a) {
    int h = a.size();
    int w = a[0].size();
    VV b(w, V(h));
    rep(i, h) {
        rep(j, w) {
            b[w - j - 1][i] = a[i][j];
        }
    }
    return b;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int H, W;
    cin >> H >> W;
    VV a(H + 2, V(W + 2, 0));
    rep2(i, 1, H + 1) {
        string s;
        cin >> s;
        rep(j, W) {
            a[i][j + 1] = (s[j] == '#' ? inf : 0);
        }
    }
    
    rep(t, 4) {
        rep2(i, 1, H + 1) {
            rep2(j, 1, W + 1) {
                a[i][j] = min<int>({a[i][j], a[i - 1][j] + 1, a[i][j - 1] + 1, a[i - 1][j - 1] + 1});
            }
        }
        a = rot(a);
        swap(H, W);
    }

    int ma = -1;
    rep(i, H + 2) ma = max(ma, *max_element(all(a[i])));
    cout << ma << endl;
}