/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.02 14:48:26
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    int h, w;
    cin >> h >> w;
    vector< string > g(h);
    vector< vector< bool > > visited(h, vector< bool >(w, false));
    queue< tuple< int, int, int > > que;
    for (int i = 0; i < h; i++) {
        cin >> g[i];
        for (int j = 0; j < w; j++) {
            if (g[i][j] == '.') {
                que.push(make_tuple(i, j, 0));
                visited[i][j] = true;
            }
        }
    }
    const int dx[] = {-1, -1, -1, 0, 0, 0, 1, 1, 1}, dy[] = {-1, 0, 1, -1, 0, 1, -1, 0, 1};
    for (int i = -1; i <= h; i++) {
        que.push(make_tuple(i, -1, 0));
        que.push(make_tuple(i, w, 0));
    }
    for (int i = 0; i < w; i++) {
        que.push(make_tuple(-1, i, 0));
        que.push(make_tuple(h, i, 0));
    }
    int ans = 0;
    while (!que.empty()) {
        auto p = que.front();
        que.pop();
        int nx = get< 0 >(p);
        int ny = get< 1 >(p);
        int d = get< 2 >(p);
        ans = max(ans, d);
        for (int i = 0; i < 8; i++) {
            int x = nx + dx[i], y = ny + dy[i];
            if (x >= 0 && x < h && y >= 0 && y < w && !visited[x][y]) {
                que.push({x, y, d + 1});
                visited[x][y] = true;
            }
        }
    }
    cout << ans << endl;
    return 0;
}