#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<LL, LL> PII;

// chmax, chmin
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

template <typename T>
function<T(T, T)> op_max = [](T a, T b) -> T { return max(a, b); };
template <typename T>
function<T(T, T)> op_min = [](T a, T b) -> T { return min(a, b); };

template <typename T>
function<T(T, T)> op_sum = [](T a, T b) -> T { return a + b; };

namespace detail {
template <typename T, std::size_t NDIMS>
struct vector_builder {
  using type = std::vector<typename vector_builder<T, NDIMS - 1>::type>;

  static type make(std::vector<std::size_t> dims, const T& v = {}) {
    const auto vec = std::vector<T>(dims.empty() ? 0 : dims.back(), v);
    if (!dims.empty()) dims.pop_back();
    return vector_builder<std::vector<T>, NDIMS - 1>::make(dims, vec);
  }
};

template <typename T>
struct vector_builder<T, 1> {
  using type = std::vector<T>;

  static type make(std::vector<std::size_t> dims, const T& v = {}) {
    return type(dims.empty() ? 0 : dims.back(), v);
  }
};
}  // namespace detail

template <typename T, typename... SIZE_T>
auto exvector(const T& v, SIZE_T... dims) {
  static_assert(sizeof...(dims) != 0, "invalid dimension");
  std::vector<std::size_t> vec_dims{dims...};
  return detail::vector_builder<T, sizeof...(dims)>::make(vec_dims, v);
}

using namespace std;
//********************  dumps ************************//

template <typename T>
void dump(const T& data, vector<int>& iter) {
  cout << data << " ";
}
template <typename T>
void dump(const vector<T>& data, vector<int>& iter) {
  for (auto elem : data) dump(elem, iter);
  cout << endl;
}

template <typename T>
void dump(const vector<vector<T>>& data, vector<int>& iter) {
  for (auto elem : iter) {
    cout << "[" << elem << "]";
  }
  cout << endl;
  for (int i = 0; i < data.size(); i++) {
    iter.push_back(i);
    dump(data[i], iter);
    iter.pop_back();
  }
  cout << endl;
}

template <typename T>
void dump(const vector<T>& data, int dummy) {
  for (int i = 0; i < data.size(); i++) {
    cout << "[" << i << "] " << data[i] << endl;
  }
}
template <typename T>
void dump(const T& data) {  // T : data, U = base type val.
  vector<int> iter;
  dump(data, iter);
}
///////////////////////////////////////////////




vector<vector<int>> calc(vector<vector<int>>& field) {
  int h = field.size();
  int w = field[0].size();
  vector<vector<int>> result(h, vector<int>(w, 10000));

  for (int i = 0; i < h; i++) {
    for (int j = 0; j < w; j++) {
      if (field[i][j] == 1) result[i][j] = 0;
      if (i > 0) {
        chmin(result[i][j], result[i - 1][j] + 1);
      }
      if (j > 0) chmin(result[i][j], result[i][j - 1] + 1);
    }
  }
  return result;
}

void solve(long long H, long long W, std::vector<std::string> A) {
  vector<vector<int>> result(H, vector<int>(W, 10000));
  vector<vector<int>> field(H, vector<int>(W, 10000));
  for(int i=0; i<H; i++) {
    for(int j=0; j<W; j++) {
      if(A[i][j] == '#') field[i][j] = 1;
    }
  }
  
  auto tmp = calc(field);
  for(int i=0; i<H; i++) {
    for(int j=0; j<W; j++)
      chmin(result[i][j], tmp[i][j]);
  }
  reverse(field.begin(), field.end());

  tmp = calc(field);
  reverse(tmp.begin(), tmp.end());
  for(int i=0; i<H; i++) {
    for(int j=0; j<W; j++)
      chmin(result[i][j], tmp[i][j]);
  }



  for(int i=0; i<H; i++) {
    reverse(field[i].begin(), field[i].end());
  }

  tmp = calc(field);
  for(int i=0; i<H; i++) {
    reverse(tmp[i].begin(), tmp[i].end());
  }
  reverse(tmp.begin(), tmp.end());
  for(int i=0; i<H; i++) {
    for(int j=0; j<W; j++)
      chmin(result[i][j], tmp[i][j]);
  }


  reverse(field.begin(), field.end());

  tmp = calc(field);
  for(int i=0; i<H; i++) {
    reverse(tmp[i].begin(), tmp[i].end());
  }
  for(int i=0; i<H; i++) {
    for(int j=0; j<W; j++)
      chmin(result[i][j], tmp[i][j]);
  }

  int ans = 0;
  for(int i=0; i<H; i++)
    for(int j=0; j<W; j++)
      chmax(ans, result[i][j]);
  cout << ans << endl;


}

int main() {
  cout << setprecision(10);
  long long H;
  scanf("%lld", &H);
  long long W;
  scanf("%lld", &W);
  std::vector<std::string> A(H);
  for (int i = 0; i < H; i++) {
    std::cin >> A[i];
  }
  solve(H, W, std::move(A));
  return 0;
}


Measured memory_bytes: 17044