#include <bits/stdc++.h>
#define SORT(a) sort(a.begin(), a.end())
#define RSORT(a) sort(a.rbegin(), a.rend())
#define REP(i, n) for (int i = 0; i < n; i++)
#define RREP(i, n) for (int i = n - 1; 0 <= i; i--)
#define FOR(i, start, end) for (int i = start; i < end; i++)
#define RFOR(i, start, end) for (int i = start - 1; 0 <= i; i--)
#define ALL(a) a.begin(), a.end()
using ll = long long;
using namespace std;
constexpr int INF32       = 1'050'000'000;
constexpr long long INF64 = 4'000'000'000'000'000'000;
constexpr int MOD7        = 1'000'000'007;
constexpr int MOD9        = 1'000'000'009;
template <class T> inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T> inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
void print() { std::cout << '\n'; }
template <class H, class... T> void print(H &&head, T &&... args) {
    std::cout << head;
    sizeof...(args) == 0 ? std::cout << "" : std::cout << ' ';
    print(std::forward<T>(args)...);
}
template <class T> void print(std::vector<T> &v) {
    for (int i = 0; i < v.size(); i++) {
        std::cout << v[i];
        i == v.size() - 1 ? std::cout << '\n' : std::cout << ' ';
    }
}
template <class T> void print(std::vector<std::vector<T>> &v) {
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            std::cout << v[i][j];
            j == v[i].size() - 1 ? std::cout << '\n' : std::cout << ' ';
        }
    }
}
void debug() { std::cerr << '\n'; }
template <class H, class... T> void debug(H &&head, T &&... args) {
    std::cerr << head;
    sizeof...(args) == 0 ? std::cerr << "" : std::cerr << ' ';
    debug(std::forward<T>(args)...);
}
template <class T> void debug(std::vector<T> &v) {
    for (int i = 0; i < v.size(); i++) {
        std::cerr << v[i];
        i == v.size() - 1 ? std::cerr << '\n' : std::cerr << ' ';
    }
}
template <class T> void debug(std::vector<std::vector<T>> &v) {
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            std::cerr << v[i][j];
            j == v[i].size() - 1 ? std::cerr << '\n' : std::cerr << ' ';
        }
    }
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int H, W;
    cin >> H >> W;
    vector<string> v(H);
    for (auto &&i : v) {
        cin >> i;
    }

    int ans        = 0;
    vector<int> dx = {-1, 1, 0, 0};
    vector<int> dy = {0, 0, -1, 1};
    auto exist     = [](int H, int W, int nx, int ny) -> bool {
        if (nx < 0 || W <= nx || ny < 0 || H <= ny)
            return false;
        else
            return true;
    };
    queue<pair<int, int>> que;
    vector<vector<bool>> vis(H, vector<bool>(W, false));
    vector<vector<int>> cnt(H, vector<int>(W, -1));

    REP(y, H) {
        REP(x, W) {
            if (v[y][x] == '#') {
                que.push({y, x});
                vis[y][x] = true;
                cnt[y][x] = 0;
            }
        }
    }

    while (!que.empty()) {
        auto a = que.front();
        int x  = a.second;
        int y  = a.first;
        que.pop();
        REP(i, dx.size()) {
            int nx = x + dx[i];
            int ny = y + dy[i];
            if (exist(H, W, nx, ny) && cnt[ny][nx] < 0) {
                cnt[ny][nx] = cnt[y][x] + 1;
                que.push({ny, nx});
            }
        }
    }
    for (auto &&i : cnt) {
        for (auto &&j : i) {
            chmax(ans, j);
        }
    }

    print(ans);

    return 0;
}


Measured memory_bytes: 13584