#include <iostream>
#include <cstdio>
#include <queue>
#define rep(i, l, r) for (int i = (l); i <= (r); i ++ )
#define per(i, r, l) for (int i = (r); i >= (l); i -- )
 
using namespace std;
 
const int N = 3005, dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
int n, m;
string ch[N];
bool st[N][N];
queue<pair<int, int> > q1, q2;
 
int main() {
 
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cin >> n >> m;
    rep(i, 1, n) {
        cin >> ch[i];
        ch[i] = '.' + ch[i] + '.';
    }
    rep(i, 0, m + 1) ch[0] += '.', ch[n + 1] += '.';
    rep(i, 0, n + 1) rep(j, 0, m + 1)
        if (ch[i][j] == '.') {
            q1.push({i, j});
            st[i][j] = 1;
        }
    int now = 0, ans = 0; 
    while (!q1.empty()) {
        swap(q1, q2);
        while (!q2.empty()) {
            auto t = q2.front(); q2.pop();
            rep(dx, -1, 1) rep(dy, -1, 1) if (dx != 0 || dy != 0) {
                int nx = t.first + dx, ny = t.second + dy;
                ans = max(ans, now);
                if (nx < 0 || ny < 0 || nx > n + 1 || ny > m + 1) continue;
                if (!st[nx][ny]) {
                    st[nx][ny] = 1;
                    q1.push({nx, ny});
                }
            }
        }
        now += 1;
    }
    printf("%d\n", ans);
 
    return 0;
}