#pragma GCC target("avx2")
#pragma GCC optimize("unroll-loops")

#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstring>
#include <deque>
#include <forward_list>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define ALL(x) (x).begin(), (x).end()

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
struct edge {
    int to, cost, id;
};
const double PI = 3.14159265358979323846;
const double PI2 = PI * 2.0;
const double EPS = 1E-09;
const ll MOD = 1E+09 + 7; // =998244353;
const ll INFL = 1E18;
const int INFI = 1E09;
const int MAX_N = 3E+03;

ll dx[4] = { -1, 1, 0, 0 }, dy[4] = { 0, 0, -1, 1 };

int H, W;

int d[MAX_N + 2][MAX_N + 2];
bool g[MAX_N + 2][MAX_N + 2];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> H >> W;

    queue<pii> que;

    fill(d[0], d[H + 2], INFI);

    for (int i = 1; i <= H; i++) {
        string s;
        cin >> s;
        for (int j = 1; j <= W; ++j) {
            if (s[j - 1] == '.') {
                que.push({ i, j });
                d[i][j] = 0;
            } else {
                g[i][j] = true;
            }
        }
    }
    for (int i = 0; i <= H + 1; ++i) {
        que.push({ i, 0 });
        que.push({ i, W + 1 });
        d[i][0] = 0;
        d[i][W + 1] = 0;
    }
    for (int j = 1; j <= W; ++j) {
        que.push({ 0, j });
        que.push({ H + 1, j });
        d[0][j] = 0;
        d[H + 1][j] = 0;
    }

    while (!que.empty()) {
        pii p = que.front();
        que.pop();
        int i = p.first;
        int j = p.second;
        for (int ii = -1; ii <= 1; ++ii) {
            for (int jj = -1; jj <= 1; ++jj) {
                int ni = i + ii, nj = j + jj;
                if (ni >= 1 && ni <= H && nj >= 1 && nj <= W && g[ni][nj] && d[ni][nj] == INFI) {
                    d[ni][nj] = d[i][j] + 1;
                    que.push({ ni, nj });
                }
            }
        }
    }

    int ans = 0;
    for (int i = 1; i <= H; ++i) {
        for (int j = 1; j <= W; ++j) {
            if (g[i][j])
                ans = max(ans, d[i][j]);
        }
    }

    // for (int i = 0; i < N; i++) {
    //     for (int j = 0; j < N; j++) {
    //         cout << "i = " << i << ", j = " << j << ", dp = " << dp[i][j] << "\n";
    //     }
    // }

    cout << ans << "\n";

    return 0;
}