#include <sstream>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <algorithm>
#include <queue>

template<typename T1, typename T2>inline std::ostream& operator << (std::ostream& os, const std::pair<T1, T2>& p) { return os << "(" << p.first << ", " << p.second << ")"; }
template<typename T>inline std::ostream &operator<<(std::ostream &os, const std::vector<T>& v) { bool first = true; os << "["; for (unsigned int i = 0; i < v.size(); i++) { if (!first)os << ", "; os << v[i]; first = false; }return os << "]"; }
inline std::ostream &operator<<(std::ostream &os, const std::vector<std::string>& v) { bool first = true; os << "["; for (unsigned int i = 0; i < v.size(); i++) { if (!first)os << ", "; os << "'" << v[i] << "'"; first = false; }return os << "]"; }
template<typename T, typename T2>void printarray(T  a[], T2 sz, T2 beg = 0) { for (T2 i = beg; i < sz; ++i) std::cout << a[i] << " "; std::cout << std::endl; }

using namespace std;

const int dx4[] = {-1, 0, 1, 0};
const int dy4[] = {0, 1, 0, -1};

const int dx8[] = {-1, 0, 1, 0 , -1 , -1 , 1 , 1};
const int dy8[] = {0, 1, 0, -1 , -1 , 1 , -1 , 1};

int main() {
    unsigned long long int H, W;
    cin >> H >> W;
    queue<pair<int,int> > que;
    string line;
    int answer = 0;
    vector<vector<int> > cnt(H, vector<int>(W, -1));
    for (int i = 0; i < H; ++i) {
        cin >> line;
        for (int j = 0; j < W; ++j) {
            if (line[j] == '.') {
                cnt[i][j] = 0;
            }
            else {
                cnt[i][j] = 1;
                que.push({i,j});
            }
        }
    }

    while(!que.empty()) {
        auto point = que.front();
        que.pop();
        int _min = 0x3f3f3f3f;
        for(int i = 0; i < 8; ++i) {
            int x = point.first + dx8[i];
            int y = point.second + dy8[i];
            if (x < 0 || x >= H || y < 0 || y >= W) {
                _min = 0;
                continue;
            }
            _min = min(_min, cnt[x][y]);
        }
        if (_min >= cnt[point.first][point.second]) {
            cnt[point.first][point.second]++;
            answer = max(answer, cnt[point.first][point.second]);
            que.push(point);
        }
    }
#if 0
    for (int i = 0; i < H; ++i) {
        for (int j = 0; j < W; ++j) {
            cout << cnt[i][j] << " ";
        }
        cout << endl;
    }
    cout << endl;
#endif
    cout << answer << endl;
    return 0;
}