#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

PII dir[4] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1} };

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

	int n, m;
	cin >> n >> m;
	vector<vector<char>> v(n + 2, vector<char>(m + 2, '-'));
	FOR(i, 0, n)
	{
		FOR(j, 0, m) cin >> v[i + 1][j + 1];
	}
	n += 2;
	m += 2;
	
	vector<VI> d(n, VI(m, -1));
	
	queue<PII> q;
	FOR(i, 0, n) FOR(j, 0, m)
	{
		if (v[i][j] == '-')
		{
			d[i][j] = 0;
			q.push({i, j});
		}
	}
	int mx = 0;
	while (!q.empty())
	{
		int x = q.front().first;
		int y = q.front().second;
		mx = max(mx, d[x][y]);
		q.pop();
		FOR(i, 0, 4)
		{
			int nx = x + dir[i].first;
			int ny = y + dir[i].second;
			if (nx >= 0 && nx < n && ny >= 0 && ny < m && d[nx][ny] == -1)
			{
				d[nx][ny] = d[x][y] + 1;
				q.push({nx, ny});
			}
			
		}
	}
	cout << mx << '\n';
	
	return 0;
}