/// Containers Start
#include <algorithm>
#include <bitset>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
/// C Header Files
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <math.h>
#include <stdio.h>
/// Containers End

using namespace std;

/// Math Start
#define PI acos(-1.0)
#define Pi 3.141592653589793
#define EPS (1e-7)
#define INF (0x3f3f3f3f)
/// Math End

/// Extra Start
#define nn '\n'
#define pb push_back
#define ull unsigned long long
#define ll long long
#define MOD 1000000007
#define sz(a) int((a).size())
#define space " "
#define All(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
/// Extra End

#define rep(i, n) for (int i = 0; i < n; i++)
#define Cini(a)                                                                \
    int a;                                                                     \
    cin >> a;
#define Cinii(a, b)                                                            \
    int a, b;                                                                  \
    cin >> a >> b;
#define Ciniii(a, b, c)                                                        \
    int a, b, c;                                                               \
    cin >> a >> b >> c;
#define Cins(s)                                                                \
    string s;                                                                  \
    cin >> s;
#define Cinss(s1, s2)                                                          \
    string s1, s2;                                                             \
    cin >> s1 >> s2;
#define Cinc(c)                                                                \
    char c;                                                                    \
    cin >> c;
/// Functions End


/// Debug Start
#define deb(x) cout << #x << ": " << x << endl
#define deb2(x, y) cout << #x << ": " << x << '\t' << #y << ": " << y << endl;
#define deb3(x, y, z)                                                          \
    cout << #x << ": " << x << '\t' << #y << ": " << y << '\t' << #z << ": "   \
         << z << endl;
/// Debug End

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

/**>>>>>>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<<<**/

/// template


signed main(void) {
    cin.sync_with_stdio(false);
    cin.tie(0);
    Cinii(H,W);
    vector<string> S(H);
    rep(i,H)cin >> S[i];
    queue<pair<int,int> > q;
    unordered_map<int,unordered_map<int,int> > m;
    rep(y,H)rep(x,W){
        if(S[y][x]=='.')continue;
        m[y][x] = 1;
        q.push(make_pair(y,x));
    }
    int ansCount = 0;
    while(q.size()>0){
        int qSize = q.size();
        bool isEdited = false;
        rep(i,qSize){
            pair<int,int> p = q.front();
            q.pop();
            rep(index,4){
                int ny = p.first+dy[index];
                int nx = p.second+dx[index];
                if(ny<0 || ny>=H) continue;
                if(nx<0 || nx>=W) continue;
                if(m[ny][nx]==1)continue;
                isEdited = true;
                m[ny][nx] = 1;
                q.push(make_pair(ny,nx));
            }
        }
        if(isEdited)ansCount++;
    }
    cout << ansCount << nn;
    return 0;
}

Measured memory_bytes: 54544