#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b)*b; }
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T> V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> > Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T> mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }

/*
 <url:>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

int solve(){
    int res = 0;
    int H,W; cin >> H >> W;
    vector<vector<char>> S(H,vector<char>(W,'.'));
    vector<vector<int>> F(H,vector<int>(W,INF));
    for(auto& vec:S) for(auto& in:vec) cin >> in;
    
    vector<pii> ps;
    for(int i = 0; i < H;i++){
        for(int j = 0; j < W;j++){
            if(S[i][j] == '.') ps.emplace_back(i,j);
        }
    }
    for(int i = 0; i < H;i++){
        for(int j = 0; j < W;j++){
            if(S[i][j] == '#'){
                int T = INF;
                for(auto p:ps){
                    T = min(T,max(abs(p.first-i),abs(p.second-j)));
                }
                res = max(res,T);
            }
        }
    }
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    cout << solve() << endl;
    return 0;
}