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

#define MAX (3000)

int H, W;
int S[MAX+2][MAX+2];

int fn(int h, int w, int (*inc)(int &,int &))
{
    int *p = &S[h][w];
    if (inc(h, w)) {
        *p = min(*p, 1);
    }
    else {
        *p = min(*p, fn(h, w, inc) + 1);
    }
    return *p;
}

int main()
{
    cin >> H;
    cin >> W;
    for (int h = 0; h < H; h++) {
        string s;
        cin >> s;
        for (int w = 0; w < W; w++) {
            if (s[w] == '.') {
                S[h][w] = 0;
            }
            else {
                S[h][w] = MAX;
            }
        }
    }
    for (int h = 0; h < H; h++) {
        fn(h, 0, [](int &hh, int &ww)->int {
            if (++ww >= W) return -1;
            return 0;
        });
        fn(h, W-1, [](int &hh, int &ww)->int {
            if (--ww < 0) return -1;
            return 0;
        });
        fn(h, 0, [](int &hh, int &ww)->int {
            if (++hh >= H || ++ww >= W) return -1;
            return 0;
        });
        fn(h, 0, [](int &hh, int &ww)->int {
            if (--hh < 0 || ++ww >= W) return -1;
            return 0;
        });
        fn(h, W-1, [](int &hh, int &ww)->int {
            if (--hh < 0 || --ww < 0) return -1;
            return 0;
        });
        fn(h, W-1, [](int &hh, int &ww)->int {
            if (++hh >= H || --ww < 0) return -1;
            return 0;
        });
    }
    for (int w = 0; w < W; w++) {
        fn(0, w, [](int &hh, int &ww)->int {
            if (++hh >= H) return -1;
            return 0;
        });
        fn(H-1, w, [](int &hh, int &ww)->int {
            if (--hh < 0) return -1;
            return 0;
        });
        fn(0, w, [](int &hh, int &ww)->int {
            if (++hh >= H || ++ww >= W) return -1;
            return 0;
        });
        fn(0, w, [](int &hh, int &ww)->int {
            if (++hh >= H || --ww < 0) return -1;
            return 0;
        });
        fn(H-1, w, [](int &hh, int &ww)->int {
            if (--hh < 0 || ++ww >= W) return -1;
            return 0;
        });
        fn(H-1, w, [](int &hh, int &ww)->int {
            if (--hh < 0 || --ww < 0) return -1;
            return 0;
        });
    }
    int ans = 0;
    for (int h = 0; h < H; h++) {
        for (int w = 0; w < W; w++) {
            ans = max(ans, S[h][w]);
        }
    }
    cout << ans << endl;
}