#include <vector>
#include <list>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <cstdio>
#include <climits>
#include <complex>
#include <cstdint>
#include <tuple>

#define M_PI       3.14159265358979323846

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
inline int readInt() { int x; scanf("%d", &x); return x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,s,n) for(int i=s;i<(int)n;++i)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()


struct Edge {
    int to, cost, nm;
    Edge(int to, int cost, int nm): to(to), cost(cost), nm(nm) {}
};

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<Edge>> AdjList;
AdjList graph;
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
const int INF = 100000000;

ll GCD(ll a, ll b){
    if(a < b) swap(a, b);
    if(b == 0) return a;
    return GCD(b, a%b);
}

bool cmp(const pii& a, const pii& b){
    if(a.first == b.first){
        return a.second < b.second;
    }
    return a.first < b.first;
}


int N, M;
double r;
int n;
int sp, gp;
vector<vector<int>> G(100010);
int dist[1010][1010];

int dxy[5] = {-1, 0, 1, 0, -1};
int main() {


    //cout << fixed << setprecision(10);

    int H, W; cin >> H >> W;

    vector<string> v;
    REP(i, H){
        string s; cin >> s;
        v.push_back(s);
    }

    vector<pii> vp;
    for(int i=0; i<H; ++i){
        for(int j=0; j<W; ++j){
            if(v[i][j] == '#'){
                vp.push_back({i, j});
            }
        }
    }
    REP(i, 1010) REP(j, 1010) dist[i][j] = -1;

    for(auto e: vp) dist[e.first][e.second] = 0;

    int ans = 0;
    for(int i=0; i<vp.size(); ++i){
        int x = vp[i].second, y = vp[i].first;
        ans = max(ans, dist[y][x]);
        for(int t = 0; t<4; ++t){
            int nx = x + dxy[t],
                ny = y + dxy[t+1];

            if(nx>=0 && nx < W && ny >= 0 && ny < H && dist[ny][nx]==-1){
                dist[ny][nx] = dist[y][x] + 1;
                vp.push_back({ny, nx});
            }
        }
    }
    cout << ans << endl;

    return 0;
}

Measured memory_bytes: 18032