#include <iostream>
#include <queue>
using namespace std;

struct State {
    int row, col, dist;

    State(int row, int col, int dist) : row(row), col(col), dist(dist) { }
};

const int kINF = 1 << 28;
const int kMAX_H = 3100;
const int kMAX_W = 3100;
string S[kMAX_H];

int dist[kMAX_H][kMAX_W];

int H, W;

bool IsIn(int row, int col) {
    return 0 <= row && row < H && 0 <= col && col < W;
}

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

    cin >> H >> W;
    for (int r = 0; r < H; r++) {
        cin >> S[r];
    }

    queue<State> que;
    fill((int* )dist, (int* )(dist + kMAX_H), kINF);
    for (int r = 0; r < H; r++) {
        for (int c = 0; c < W; c++) {
            if (S[r][c] == '.') {
                que.push(State(r, c, 0));
                dist[r][c] = 0;
            }
        }
    }
    while (!que.empty()) {
        State s = que.front(); que.pop();
        for (int dr = -1; dr <= 1; dr++) {
            for (int dc = -1; dc <= 1; dc++) {
                int nr = s.row + dr, nc = s.col + dc;
                if (IsIn(nr, nc) && S[nr][nc] == '#' && dist[nr][nc] == kINF) {
                    que.push(State(nr, nc, s.dist + 1));
                    dist[nr][nc] = s.dist + 1;
                }
            }
        }
    }

    int ans = 0;
    for (int r = 0; r < H; r++) {
        for (int c = 0; c < W; c++) {
            if (S[r][c] == '.') continue;
            /*
            if (S[r][c] == '.') {
                cout << "x ";
                continue;
            }
            */
            int move_r = min(r, H - 1 - r) + 1,
                move_c = min(c, W - 1 - c) + 1,
                c_dist = min(move_r, move_c);
            ans = max(ans, min(dist[r][c], c_dist));
            // cout << min(dist[r][c], c_dist) << " ";
        }
        // cout << endl;
    }
    cout << ans << endl;

    return 0;
}