#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define REP1(i, n) for(int i=1; i<=(n); i++)
#define RREP1(i, n) for(int i=(n); i>=1; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define out(...) printf(__VA_ARGS__)
#define chmax(a,b) a = max(a,b)
#define chmin(a,b) a = min(a,b)
#if DEBUG
#define debug(...) printf(__VA_ARGS__)
#else
#define debug(...) /* ... */
#endif

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/
#if DEBUG
#define SIZE 100
#else
#define SIZE 3333
#endif

int H,W;
string M[SIZE];
int DP[SIZE][SIZE];
int dxs[] = {1,1,1,0,-1,-1,-1,0};
int dys[] = {1,0,-1,-1,-1,0,1,1};

void solve() {
    cin>>H>>W;
    REP(h,H)cin>>M[h];
    REP(h,H)REP(w,W)DP[h][w]=INT_MAX;
    queue<pair<int,int>> que;
    REP(h,H)REP(w,W)if(M[h][w]=='.'){
        DP[h][w]=0;
        que.push({h,w});
    }
    REP(h,H) {
        if (DP[h][0]) que.push({h,0}), DP[h][0]=1;
        if (DP[h][W-1]) que.push({h,W-1}), DP[h][W-1]=1;
    }
    REP(w,W) {
        if (DP[0][w]) que.push({0,w}), DP[0][w]=1;
        if (DP[H-1][0]) que.push({H-1,w}), DP[H-1][w]=1;
    }
    while(que.size()) {
        auto p = que.front();
        int h = p.first, w = p.second;
        que.pop();
        REP(i,8) {
            int dh = dxs[i], dw = dys[i];
            int nh = h+dh, nw = w+dw;
            if (nh<0||nw<0||nh>=H||nw>=W) continue;
            int nv = DP[h][w]+1;
            if (DP[nh][nw]>nv) {
                DP[nh][nw]=nv;
                que.push({nh,nw});
            }
        }
    }
    int ans = 0;
    REP(h,H)REP(w,W)chmax(ans,DP[h][w]);
    cout << ans << endl;
}