#include <iostream>
#include <vector>
#include <deque>
using namespace std;

int main() {
    int H, W;
    cin >> H >> W;
    vector<string> lsHW(H + 2, string(W + 2, '.'));
    for (int i = 1; i <= H; ++i) {
        string row;
        cin >> row;
        lsHW[i] = '.' + row + '.';
    }
    H += 2;
    W += 2;
    const int INF = 5000;
    vector<vector<int>> cost(H, vector<int>(W, INF));
    vector<pair<int, int>> dxy = {{0, 1}, {1, 0}, {-1, 0}, {0, -1}, {1, 1}, {-1, 1}, {1, -1}, {-1, -1}};
    deque<pair<int, int>> d;
    for (int i = 0; i < H; ++i) {
        for (int j = 0; j < W; ++j) {
            if (lsHW[i][j] == '.') {
                cost[i][j] = 0;
                d.emplace_back(i, j);
            }
        }
    }
    int cmax = 0;
    while (!d.empty()) {
        int x = d.front().first;
        int y = d.front().second;
        d.pop_front();
        for (const auto& dxdy : dxy) {
            int dx = dxdy.first;
            int dy = dxdy.second;
            if (0 <= x + dx && x + dx < H && 0 <= y + dy && y + dy < W) {
                if (cost[x + dx][y + dy] > cost[x][y] + 1) {
                    cost[x + dx][y + dy] = cost[x][y] + 1;
                    cmax = cost[x][y] + 1;
                    d.emplace_back(x + dx, y + dy);
                }
            }
        }
    }
    cout << cmax << endl;
    return 0;
}