#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <map>
#include <iostream>
#include <queue>
#include <stack>
#include <algorithm>
#include <deque>
#include <fstream>
#include <functional>
#include <cctype>
#include <unordered_set>
#include <unordered_map>

using namespace std;

#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i = 0; i < (n); i++)
#define repr(i,b,e) for(int i = (b); i <= (e); i++)

#define pr(x) do{cerr << (#x) << " = " << (x) << endl;}while(0)
#define pri(x,i) do{cerr << (#x) << "[" << i << "] = " << (x[i]) << endl;}while(0)

namespace std {
	template<class S, class T> pair<S, T> operator + (const pair<S, T> &a, const pair<S, T> &b) {return mp<S, T>(a.first + b.first, a.second + b.second);}
	template<class S, class T> pair<S, T> operator - (const pair<S, T> &a, const pair<S, T> &b) {return mp<S, T>(a.first - b.first, a.second - b.second);}
	template<class S, class T> pair<S, T>& operator += (pair<S, T> &a, const pair<S, T> &other) {return a = a + other;}
	template<class S, class T> pair<S, T>& operator -= (pair<S, T> &a, const pair<S, T> &other) {return a = a - other;}
	template<class S, class T> ostream& operator << (ostream& ost, pair<S, T> p) {ost << "(" << p.first << ", " << p.second << ")";return ost;}
	template<class T> ostream& print_iterable_container(ostream& ost, T& container) {
		for (auto&& iter = begin(container); iter != end(container); ++iter) ost << (iter == begin(container) ? " [ " : ", ") << (*iter);
		return ost << " ]";
	}
#	define APPLY_PRINT_ITERABLE_CONTAINER(container_type)\
	template<class T> ostream& operator << (ostream& ost, container_type<T>& container) {\
		return print_iterable_container(ost, container);\
	}
	APPLY_PRINT_ITERABLE_CONTAINER(vector);
	APPLY_PRINT_ITERABLE_CONTAINER(list);
	APPLY_PRINT_ITERABLE_CONTAINER(deque);
}

template<class T> inline bool CHMAX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool CHMIN(T &l,const T &r){return l>r?l=r,1:0;}

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using vpii = vector<pii>;
using vpll = vector<pll>;

using ld = long double;

template<class T> using VV = vector<vector<T> >;
template<class T> using maxPQ = priority_queue<T>;
template<class T> using minPQ = priority_queue<T, vector<T>, greater<T> >;
template<class T, class U> using uomap = unordered_map<T, U>;
template<class T> using uoset = unordered_set<T>;

const ll INF = 1001001001;
const ll INFll = (ll)INF * INF;
const ll MOD = 1000000007;
const ll MOD_FFT = 998244353;
const ld EPS = 1e-15;

//function<void(int,int)> tensi_no_3p=[&](int v,int d){
//};

vvi A, cnt;
int H, W;

inline bool isranged(int r, int c) {
	return r >= 0 && r < H && c >= 0 && c < W;
}

int main() {
	ios_base::sync_with_stdio(false);
	queue<pair<int, pii> > Q;
	cin >> H >> W;
	A.resize(H);
	rep(i, H) {
		A[i].resize(W);
		string s;
		cin >> s;
		rep(k, W) {
			A[i][k] = s[k] == '#' ? 1 : 0;
			if (A[i][k]) Q.push(mp(0, mp(i, k)));
		}
	}
	cnt.resize(H);
	rep(i, H) cnt[i].resize(W, INF);
	while (! Q.empty()) {
		auto t = Q.front(); Q.pop();
		if (isranged(t.second.first, t.second.second) && t.first < cnt[t.second.first][t.second.second]) {
			cnt[t.second.first][t.second.second] = t.first;
			int hoge = t.first + 1;
			Q.push(mp(hoge, mp(t.second.first - 1, t.second.second)));
			Q.push(mp(hoge, mp(t.second.first + 1, t.second.second)));
			Q.push(mp(hoge, mp(t.second.first, t.second.second - 1)));
			Q.push(mp(hoge, mp(t.second.first, t.second.second + 1)));
		}
	}
	int ans = 0;
	rep(i, H) rep(k, W) CHMAX(ans, cnt[i][k]);

	cout << ans << endl;
	return 0;
}


Measured memory_bytes: 56520