#include <bits/stdc++.h>
using namespace std;

#define REP(i,n) for(int i=0;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)
#define INF 1<<29
#define LINF LLONG_MAX/3
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(v) (v).begin(),(v).end()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;

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

int H,W;
vector<string> S;

int dis(pii a,pii b){
    int x = abs(a.first - b.first);
    int y = abs(a.second - b.second);
    return max(x,y);
}

int main(){
    set<pii> sea,land;
    cin >> H >> W;
    S.resize(H+2);
    for(int i=1;i<=H;i++){
        string s;cin>>s;
        S[i] = "." + s + ".";
    }
    string dot(W+2,'.');
    S[0]=dot;
    S[H+1]=dot;

    for(int i=0;i<S.size();i++){
        for(int j=0;j<S[i].size();j++){
            if(S[i][j]=='.') sea.insert(MP(i,j));
            else land.insert(MP(i,j));
        }
    }


    int ans = 1;
    for(pii v:land){
        int dmin=INF;
        for(pii u:sea){
            dmin= min(dmin,dis(u,v));
        }
        ans = max(ans,dmin);
    }
    cout << ans << endl;
}