#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={0,1,-1,0,1,1,-1,-1,0};
const ll dx[9]={1,0,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
int main(){
    ll h,w;cin >> h >> w;
    vector<vector<char>> g(h+2,vector<char>(w+2,'.'));
    rep(i,h)rep(j,w)cin >> g[i+1][j+1];
    h+=2;w+=2;
    queue<ll> que;
    vl dist(h*w,-1);
    rep(i,h)rep(j,w){
        if(g[i][j]!='.')continue;
        que.push(i*w+j);
        dist[i*w+j]=0LL;
    }
    while(!que.empty()){
        ll v=que.front();que.pop();
        ll x=v/w,y=v%w;
        rep(i,8){
            ll nx=x+dx[i];
            ll ny=y+dy[i];
            if(nx<0||ny<0||nx>=h||ny>=w)continue;
            ll next=nx*w+ny;
            if(dist[next]!=-1)continue;
            dist[next]=dist[v]+1;
            que.push(next);
        }
    }
    ll ans=0;
    rep(i,h)rep(j,w)chmax(ans,dist[i*w+j]);
    cout << ans << endl;
}