#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

#define pb push_back

const ld pi = 3.14159265358979323846;
const ll INF = 1e18;
const int mod = (int)1e9 + 7;

template<typename T>
T chmax(T a, T b) {
    return a > b ? a : b;
}

template<typename T>
T chmin(T a, T b) {
    return a > b ? b : a;
}

const int N = 3e3 + 1, M = N * 2;

int dirx[4] = {0, 0, 1, -1}, diry[4] = {1, -1, 0, 0};

void solve() {
    int n, m;
    cin >> n >> m;

    char c[n][m];
    for(int i = 0; i < n; i++){
        string s;
        cin >> s;
        for(int j = 0; j < m; j++){
            c[i][j] = s[j];
        }
    }

    int qwq = 0;
    while(1){
        queue<pair<int, int>> q;

        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                int x = i, y = j;
                int owo = 0;

                if(c[i][j] != 'X'){
                    continue;
                }
                for(int k = 0; k < 4; k++){
                    int dx = x + dirx[k], dy = y + diry[k];
                    if(dx < 0 || dy < 0 || dx >= n || dy >= m){
                        owo++;
                        continue;
                    }
                    if(c[dx][dy] != 'X'){
                        owo++;
                    }
                }
                if(owo){
                    q.push({x, y});
                }
            }
        }

        if(!q.empty()){
            qwq++;
        }
        else{
            break;
        }

        while(!q.empty()){
            auto p = q.front();
            q.pop();

            c[p.first][p.second] = '-';
        }
    }
    cout << qwq << endl;
}

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

    int t = 1;
    // cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}