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

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

int H,W;
char fld[3010][3010];

int dist[3010][3010];

signed main(){
    scanf("%lld%lld",&H,&W);
    rep(i,H)scanf("%s",fld[i]);

    memset(dist,-1,sizeof(dist));

    queue<pint>que;

    rep(i,H)rep(j,W){
        if(fld[i][j]=='.'){
            dist[i][j]=0;
            que.push(pint(i,j));
        }
        else if(fld[i][j]=='#'&&(i==0||i==H-1||j==0||j==W-1)){
            dist[i][j]=1;
            que.push(pint(i,j));
        }
    }
    while(que.size()){
        int y,x;
        tie(y,x)=que.front();
        que.pop();
        for(int dy=-1;dy<=1;dy++){
            for(int dx=-1;dx<=1;dx++){
                int ny=y+dy,nx=x+dx;
                if(ny<0||ny>=H||nx<0||nx>=W||dist[ny][nx]!=-1)continue;
                dist[ny][nx]=dist[y][x]+1;
                que.push(pint(ny,nx));
            }
        }
    }
    int ma=0;
    rep(i,H)rep(j,W)chmax(ma,dist[i][j]);
    cout<<ma<<endl;
    return 0;
}