#include <bits/stdc++.h>
using namespace std;
struct Fast {
    Fast() {
        std::cin.tie(0);
        ios::sync_with_stdio(false);
        cout.precision(20);
    }
} fast;

/* define */
#define FOR(I, X, Y) for(long long(I) = (X); (I) < (Y); (I)++)
#define REP(I, X, Y) for(long long(I) = (Y)-1; (I) >= (X); (I)--)
#define ALL(X) (X).begin(), (X).end()
#define pb push_back
#define COUNT(V, X)                                                            \
    (upper_bound((V).begin(), (V).end(), X) -                                  \
     lower_bound((V).begin(), (V).end(), X))
#define debug(x) cerr << #x << ':' << x << endl;
#define DEBUG(v)                                                               \
    {                                                                          \
        cerr << #v << ':';                                                     \
        for(auto xv : v) cerr << xv << ' ';                                    \
        cerr << endl;                                                          \
    }
#define Yes(X) cout << (X ? "Yes" : "No") << endl;
#define YES(X) cout << (X ? "YES" : "NO") << endl;
#define ctoi(C) (C - '0')
#define pow2(x) ((long long)((long long)1 << x))

/* alias */
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<long long>;
using vll = vector<vector<long long>>;
using pi = pair<int, int>;
using pl = pair<long long, long long>;
template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const long long dx[] = {1, 0, -1, 0};
const long long dy[] = {0, 1, 0, -1};
const long long dx8[] = {1, 1, 0, -1, -1, -1, 0, 1};
const long long dy8[] = {0, 1, 1, 1, 0, -1, -1, -1};
const long long dx9[] = {1, 1, 0, -1, -1, -1, 0, 1, 0};
const long long dy9[] = {0, 1, 1, 1, 0, -1, -1, -1, 0};
const int INF = 1000000007;
const long long LINF = 1000000000000000007;

/* func */
template <typename T> inline bool chmin(T &a, const T &b) {
    if(a > b) a = b;
    return a > b;
}
template <typename T> inline bool chmax(T &a, const T &b) {
    if(a < b) a = b;
    return a < b;
}
long long max(long long x, int y) {
    return max(x, (long long)y);
}
long long max(int x, long long y) {
    return max((long long)x, y);
}
long long min(long long x, int y) {
    return min(x, (long long)y);
}
long long min(int x, long long y) {
    return min((long long)x, y);
}

/* liblary */

/* main */

signed main() {
    ll H, W;
    cin >> H >> W;
    char A[H][W];
    FOR(i, 0, H) FOR(j, 0, W) cin >> A[i][j];
    ll bfs[H][W];
    FOR(i, 0, H) FOR(j, 0, W) bfs[i][j] = -1;
    queue<pi> que;
    FOR(i, 0, H) FOR(j, 0, W) {
        if(A[i][j] == '#') {
            bfs[i][j] = 0;
            que.push(make_pair(i, j));
        }
    }
    while(que.size()) {
        int f = que.front().first;
        int s = que.front().second;
        que.pop();
        FOR(i, 0, 4) {
            if(0 <= f + dx[i] && f + dx[i] < H && 0 <= s + dy[i] &&
               s + dy[i] < W) {
                if(bfs[f + dx[i]][s + dy[i]] == -1) {
                    que.push(make_pair(f + dx[i], s + dy[i]));
                    bfs[f + dx[i]][s + dy[i]] = bfs[f][s] + 1;
                }
            }
        }
    }
    ll ans = 0;
    FOR(i, 0, H) FOR(j, 0, W) chmax(ans, bfs[i][j]);
    cout << ans << endl;
}

Measured memory_bytes: 17296