#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define mem(a) memset(a,0,sizeof(a))
#define pd(a) printf("%.10f\n",a)
#define pb(a) push_back(a)
#define in(a) insert(a)
#define pi M_PI
#define R cin>>
#define F first
#define S second
#define C class
#define ll long long
#define ln cout<<'\n'
template<C T>void pr(T a){cout<<a;ln;}
template<C T,C T2>void pr(T a,T2 b){cout<<a<<' '<<b;ln;}
template<C T,C T2,C T3>void pr(T a,T2 b,T3 c){cout<<a<<' '<<b<<' '<<c;ln;}
template<C T>void PR(T a,int n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[8]={-1,0,1,-1,1,-1,0,1},dy[8]={-1,-1,-1,0,0,1,1,1};
typedef pair<int,int> P;

int d[3010][3010];
string s[3010];

void Main() {
  int n,m;
  cin >> n >> m;
  rep(j,m+2) s[0]+='.';
  rep(j,m+2) s[n+1]+='.';
  REP(i,1,n+1) {
    cin >> s[i];
    s[i]='.'+s[i]+'.';
  }
  n=n+2,m=m+2;
  rep(i,n)rep(j,m) d[i][j]=MAX;
  queue<P> que;
  rep(i,n) {
    rep(j,m) {
      if(s[i][j]=='.') {
        d[i][j]=0;
        que.push(P(i,j));
      }
    }
  }
  while(!que.empty()) {
    P p=que.front();que.pop();
    int xx=p.F,yy=p.S;
    rep(i,8) {
      int x=xx+dx[i],y=yy+dy[i];
      if(!check(n,m,x,y)||d[x][y]<=d[xx][yy]+1) continue;
      d[x][y]=d[xx][yy]+1;
      que.push(P(x,y));
    }
  }
  int ans=0;
  rep(i,n)rep(j,m)ans=max(ans,d[i][j]);
  pr(ans);
}

int main() {
  ios::sync_with_stdio(0);cin.tie(0);
  Main();return 0;
}