#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)

typedef long long ll;
int H, W;
string S[3010];
//-----------------------------------------------------------------
struct Comp {
	bool operator() (pair<int, ll> a, pair<int, ll> b) {
		return a.second > b.second;
	}
};
#define INF INT_MAX/2
int dx[8] = { 0,1,1,1,0,-1,-1,-1 };
int dy[8] = { -1,-1,0,1,1,1,0,-1 };
bool done[3010][3010];
ll dist[3010][3010];
ll solve() {
	priority_queue<pair<int, ll>, vector<pair<int, ll> >, Comp> que;

	rep(y, 0, H) rep(x, 0, W) dist[y][x] = INF;

	rep(y, 0, H) rep(x, 0, W) {
		if ((x != 0 && x != W - 1) && (y != 0 && y != H - 1)) continue;

		if (S[y][x] == '#') {
			dist[y][x] = 1;
			done[y][x] = true;
			que.push(make_pair(y * 10000 + x, 1));
		}
	}

	rep(y, 0, H) rep(x, 0, W) if(S[y][x] == '.'){
		dist[y][x] = 0;
		done[y][x] = true;
		que.push(make_pair(y * 10000 + x, 0));
	}

	while (!que.empty()) {
		auto q = que.top(); que.pop();

		int x = q.first % 10000;
		int y = q.first / 10000;
		ll c = q.second;

		rep(i, 0, 8) {
			int yy = y + dy[i];
			int xx = x + dx[i];
			if (yy < 0 || H <= yy) continue;
			if (xx < 0 || W <= xx) continue;
			if (done[yy][xx]) continue;

			int cc = c + 1;

			if (S[yy][xx] == '.') cc = 0;

			if (cc < dist[yy][xx]) {
				dist[yy][xx] = cc;
				done[yy][xx] = true;
				que.push(make_pair(yy * 10000 + xx, cc));
			}
		}
	}

	ll ans = 0;
	rep(y, 0, H) rep(x, 0, W) ans = max(ans, dist[y][x]);
	return ans;
}
//-----------------------------------------------------------------
int main()
{
	cin >> H >> W;
	rep(y, 0, H) cin >> S[y];

	cout << solve() << endl;
}