#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <functional>

using namespace std;

#define fst first
#define scd second
#define PB push_back
#define MP make_pair
#define rep(i,x) for(int i=0;i<(x);++i)
#define rep1(i,x) for(int i=1;i<=(x);++i)
#define rrep(i,x) for(int i=(x)-1;i>=0;--i)
#define rrep1(i,x) for(int i=(x);i>=1;--i)
#define int long long
#define FOR(i,a,x) for(int i=(a);i<(x);++i)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define omajinai ios::sync_with_stdio(false);cin.tie(0)

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;

template<typename T>T& max(T&a,T&b){if(a>=b)return a;return b;}
template<typename T>T& min(T&a,T&b){if(a<b)return a;return b;}
template<typename T>bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<typename T>T get(){T a;cin>>a;return a;}
template<typename T>T rev(T a){reverse(all(a));return a;}
template<typename T>istream&operator>>(istream&is,vector<T>&vec){rep(i,vec.size())is>>vec[i];return is;}
template<typename T>vector<T>&sort(vector<T>&a){sort(all(a));return a;}

const int inf = 1e9;
const ll linf = 3e18;
const double eps = 1e-9;

bool used[3003][3003];
int dist[3003][3003];

struct data {
    pii p;
    int d;
    data(){}
    data(pii p, int d):p(p),d(d){}
};

int dx[8] = {-1, 0, 1, -1, 1, -1, 0, 1}, dy[8] = {-1, -1, -1, 0, 0, 1, 1, 1};

signed main()
{
    int H, W; cin >> H >> W;

    memset(dist, -1, sizeof(dist));

    rep1(i, H) {
        rep1(j, W) {
            char c;
            scanf("\n%c", &c);
            dist[i][j] = (c == '#') ? inf : -1;
        }
    }

    queue<data> que;

    rep(i, H + 2) {
        rep(j, W + 2) {
            if (dist[i][j] == -1) {
                que.push((data){(pii){i, j}, 0});
                dist[i][j] = 0;
                used[i][j] = true;
            }
        }
    }

    while (que.size()) {
        data da = que.front(); que.pop();

        rep(i, 8) {
            int ny = da.p.fst + dy[i], nx = da.p.scd + dx[i];

            if (ny < 0 || ny >= H + 2 || nx < 0 || nx >= W + 2) continue;
            if (used[ny][nx]) continue;

            int nd = da.d + 1;

            dist[ny][nx] = nd;

            que.push((data){(pii){ny, nx}, nd});

            used[ny][nx] = true;
        }
    }

    int ma = 0;
    rep(i, H + 2) rep(j, W + 2) chmax(ma, dist[i][j]);

    cout << ma << endl;
}